| 1 | RAID arrays
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| 2 | ===========
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| 3 |
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| 4 | Boot time assembly of RAID arrays
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| 5 | ---------------------------------
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| 6 |
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| 7 | Tools that manage md devices can be found at
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| 8 | https://www.kernel.org/pub/linux/utils/raid/
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| 9 |
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| 10 |
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| 11 | You can boot with your md device with the following kernel command
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| 12 | lines:
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| 13 |
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| 14 | for old raid arrays without persistent superblocks::
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| 15 |
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| 16 | md=<md device no.>,<raid level>,<chunk size factor>,<fault level>,dev0,dev1,...,devn
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| 17 |
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| 18 | for raid arrays with persistent superblocks::
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| 19 |
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| 20 | md=<md device no.>,dev0,dev1,...,devn
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| 21 |
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| 22 | or, to assemble a partitionable array::
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| 23 |
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| 24 | md=d<md device no.>,dev0,dev1,...,devn
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| 25 |
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| 26 | ``md device no.``
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| 27 | +++++++++++++++++
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| 28 |
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| 29 | The number of the md device
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| 30 |
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| 31 | ================= =========
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| 32 | ``md device no.`` device
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| 33 | ================= =========
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| 34 | 0 md0
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| 35 | 1 md1
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| 36 | 2 md2
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| 37 | 3 md3
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| 38 | 4 md4
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| 39 | ================= =========
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| 40 |
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| 41 | ``raid level``
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| 42 | ++++++++++++++
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| 43 |
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| 44 | level of the RAID array
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| 45 |
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| 46 | =============== =============
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| 47 | ``raid level`` level
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| 48 | =============== =============
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| 49 | -1 linear mode
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| 50 | 0 striped mode
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| 51 | =============== =============
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| 52 |
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| 53 | other modes are only supported with persistent super blocks
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| 54 |
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| 55 | ``chunk size factor``
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| 56 | +++++++++++++++++++++
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| 57 |
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| 58 | (raid-0 and raid-1 only)
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| 59 |
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| 60 | Set the chunk size as 4k << n.
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| 61 |
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| 62 | ``fault level``
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| 63 | +++++++++++++++
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| 64 |
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| 65 | Totally ignored
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| 66 |
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| 67 | ``dev0`` to ``devn``
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| 68 | ++++++++++++++++++++
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| 69 |
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| 70 | e.g. ``/dev/hda1``, ``/dev/hdc1``, ``/dev/sda1``, ``/dev/sdb1``
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| 71 |
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| 72 | A possible loadlin line (Harald Hoyer <[email protected]>) looks like this::
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| 73 |
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| 74 | e:\loadlin\loadlin e:\zimage root=/dev/md0 md=0,0,4,0,/dev/hdb2,/dev/hdc3 ro
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| 75 |
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| 76 |
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| 77 | Boot time autodetection of RAID arrays
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| 78 | --------------------------------------
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| 79 |
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| 80 | When md is compiled into the kernel (not as module), partitions of
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| 81 | type 0xfd are scanned and automatically assembled into RAID arrays.
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| 82 | This autodetection may be suppressed with the kernel parameter
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| 83 | ``raid=noautodetect``. As of kernel 2.6.9, only drives with a type 0
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| 84 | superblock can be autodetected and run at boot time.
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| 85 |
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| 86 | The kernel parameter ``raid=partitionable`` (or ``raid=part``) means
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| 87 | that all auto-detected arrays are assembled as partitionable.
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| 88 |
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| 89 | Boot time assembly of degraded/dirty arrays
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| 90 | -------------------------------------------
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| 91 |
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| 92 | If a raid5 or raid6 array is both dirty and degraded, it could have
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| 93 | undetectable data corruption. This is because the fact that it is
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| 94 | ``dirty`` means that the parity cannot be trusted, and the fact that it
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| 95 | is degraded means that some datablocks are missing and cannot reliably
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| 96 | be reconstructed (due to no parity).
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| 97 |
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| 98 | For this reason, md will normally refuse to start such an array. This
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| 99 | requires the sysadmin to take action to explicitly start the array
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| 100 | despite possible corruption. This is normally done with::
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| 101 |
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| 102 | mdadm --assemble --force ....
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| 103 |
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| 104 | This option is not really available if the array has the root
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| 105 | filesystem on it. In order to support this booting from such an
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| 106 | array, md supports a module parameter ``start_dirty_degraded`` which,
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| 107 | when set to 1, bypassed the checks and will allows dirty degraded
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| 108 | arrays to be started.
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| 109 |
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| 110 | So, to boot with a root filesystem of a dirty degraded raid 5 or 6, use::
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| 111 |
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| 112 | md-mod.start_dirty_degraded=1
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| 113 |
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| 114 |
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| 115 | Superblock formats
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| 116 | ------------------
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| 117 |
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| 118 | The md driver can support a variety of different superblock formats.
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| 119 | Currently, it supports superblock formats ``0.90.0`` and the ``md-1`` format
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| 120 | introduced in the 2.5 development series.
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| 121 |
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| 122 | The kernel will autodetect which format superblock is being used.
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| 123 |
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| 124 | Superblock format ``0`` is treated differently to others for legacy
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| 125 | reasons - it is the original superblock format.
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| 126 |
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| 127 |
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| 128 | General Rules - apply for all superblock formats
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| 129 | ------------------------------------------------
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| 130 |
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| 131 | An array is ``created`` by writing appropriate superblocks to all
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| 132 | devices.
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| 133 |
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| 134 | It is ``assembled`` by associating each of these devices with an
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| 135 | particular md virtual device. Once it is completely assembled, it can
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| 136 | be accessed.
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| 137 |
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| 138 | An array should be created by a user-space tool. This will write
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| 139 | superblocks to all devices. It will usually mark the array as
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| 140 | ``unclean``, or with some devices missing so that the kernel md driver
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| 141 | can create appropriate redundancy (copying in raid 1, parity
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| 142 | calculation in raid 4/5).
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| 143 |
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| 144 | When an array is assembled, it is first initialized with the
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| 145 | SET_ARRAY_INFO ioctl. This contains, in particular, a major and minor
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| 146 | version number. The major version number selects which superblock
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| 147 | format is to be used. The minor number might be used to tune handling
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| 148 | of the format, such as suggesting where on each device to look for the
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| 149 | superblock.
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| 150 |
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| 151 | Then each device is added using the ADD_NEW_DISK ioctl. This
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| 152 | provides, in particular, a major and minor number identifying the
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| 153 | device to add.
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| 154 |
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| 155 | The array is started with the RUN_ARRAY ioctl.
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| 156 |
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| 157 | Once started, new devices can be added. They should have an
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| 158 | appropriate superblock written to them, and then be passed in with
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| 159 | ADD_NEW_DISK.
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| 160 |
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| 161 | Devices that have failed or are not yet active can be detached from an
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| 162 | array using HOT_REMOVE_DISK.
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| 163 |
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| 164 |
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| 165 | Specific Rules that apply to format-0 super block arrays, and arrays with no superblock (non-persistent)
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| 166 | --------------------------------------------------------------------------------------------------------
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| 167 |
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| 168 | An array can be ``created`` by describing the array (level, chunksize
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| 169 | etc) in a SET_ARRAY_INFO ioctl. This must have ``major_version==0`` and
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| 170 | ``raid_disks != 0``.
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| 171 |
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| 172 | Then uninitialized devices can be added with ADD_NEW_DISK. The
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| 173 | structure passed to ADD_NEW_DISK must specify the state of the device
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| 174 | and its role in the array.
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| 175 |
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| 176 | Once started with RUN_ARRAY, uninitialized spares can be added with
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| 177 | HOT_ADD_DISK.
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| 178 |
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| 179 |
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| 180 | MD devices in sysfs
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| 181 | -------------------
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| 182 |
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| 183 | md devices appear in sysfs (``/sys``) as regular block devices,
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| 184 | e.g.::
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| 185 |
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| 186 | /sys/block/md0
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| 187 |
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| 188 | Each ``md`` device will contain a subdirectory called ``md`` which
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| 189 | contains further md-specific information about the device.
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| 190 |
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| 191 | All md devices contain:
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| 192 |
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| 193 | level
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| 194 | a text file indicating the ``raid level``. e.g. raid0, raid1,
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| 195 | raid5, linear, multipath, faulty.
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| 196 | If no raid level has been set yet (array is still being
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| 197 | assembled), the value will reflect whatever has been written
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| 198 | to it, which may be a name like the above, or may be a number
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| 199 | such as ``0``, ``5``, etc.
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| 200 |
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| 201 | raid_disks
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| 202 | a text file with a simple number indicating the number of devices
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| 203 | in a fully functional array. If this is not yet known, the file
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| 204 | will be empty. If an array is being resized this will contain
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| 205 | the new number of devices.
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| 206 | Some raid levels allow this value to be set while the array is
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| 207 | active. This will reconfigure the array. Otherwise it can only
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| 208 | be set while assembling an array.
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| 209 | A change to this attribute will not be permitted if it would
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| 210 | reduce the size of the array. To reduce the number of drives
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| 211 | in an e.g. raid5, the array size must first be reduced by
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| 212 | setting the ``array_size`` attribute.
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| 213 |
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| 214 | chunk_size
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| 215 | This is the size in bytes for ``chunks`` and is only relevant to
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| 216 | raid levels that involve striping (0,4,5,6,10). The address space
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| 217 | of the array is conceptually divided into chunks and consecutive
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| 218 | chunks are striped onto neighbouring devices.
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| 219 | The size should be at least PAGE_SIZE (4k) and should be a power
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| 220 | of 2. This can only be set while assembling an array
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| 221 |
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| 222 | layout
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| 223 | The ``layout`` for the array for the particular level. This is
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| 224 | simply a number that is interpreted differently by different
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| 225 | levels. It can be written while assembling an array.
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| 226 |
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| 227 | array_size
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| 228 | This can be used to artificially constrain the available space in
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| 229 | the array to be less than is actually available on the combined
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| 230 | devices. Writing a number (in Kilobytes) which is less than
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| 231 | the available size will set the size. Any reconfiguration of the
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| 232 | array (e.g. adding devices) will not cause the size to change.
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| 233 | Writing the word ``default`` will cause the effective size of the
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| 234 | array to be whatever size is actually available based on
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| 235 | ``level``, ``chunk_size`` and ``component_size``.
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| 236 |
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| 237 | This can be used to reduce the size of the array before reducing
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| 238 | the number of devices in a raid4/5/6, or to support external
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| 239 | metadata formats which mandate such clipping.
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| 240 |
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| 241 | logical_block_size
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| 242 | Configure the array's logical block size in bytes. This attribute
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| 243 | is only supported for 1.x meta. Write the value before starting
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| 244 | array. The final array LBS uses the maximum between this
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| 245 | configuration and LBS of all combined devices. Note that
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| 246 | LBS cannot exceed PAGE_SIZE before RAID supports folio.
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| 247 | WARNING: Arrays created on new kernel cannot be assembled at old
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| 248 | kernel due to padding check, Set module parameter 'check_new_feature'
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| 249 | to false to bypass, but data loss may occur.
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| 250 |
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| 251 | reshape_position
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| 252 | This is either ``none`` or a sector number within the devices of
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| 253 | the array where ``reshape`` is up to. If this is set, the three
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| 254 | attributes mentioned above (raid_disks, chunk_size, layout) can
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| 255 | potentially have 2 values, an old and a new value. If these
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| 256 | values differ, reading the attribute returns::
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| 257 |
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| 258 | new (old)
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| 259 |
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| 260 | and writing will effect the ``new`` value, leaving the ``old``
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| 261 | unchanged.
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| 262 |
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| 263 | component_size
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| 264 | For arrays with data redundancy (i.e. not raid0, linear, faulty,
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| 265 | multipath), all components must be the same size - or at least
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| 266 | there must a size that they all provide space for. This is a key
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| 267 | part or the geometry of the array. It is measured in sectors
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| 268 | and can be read from here. Writing to this value may resize
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| 269 | the array if the personality supports it (raid1, raid5, raid6),
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| 270 | and if the component drives are large enough.
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| 271 |
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| 272 | metadata_version
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| 273 | This indicates the format that is being used to record metadata
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| 274 | about the array. It can be 0.90 (traditional format), 1.0, 1.1,
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| 275 | 1.2 (newer format in varying locations) or ``none`` indicating that
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| 276 | the kernel isn't managing metadata at all.
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| 277 | Alternately it can be ``external:`` followed by a string which
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| 278 | is set by user-space. This indicates that metadata is managed
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| 279 | by a user-space program. Any device failure or other event that
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| 280 | requires a metadata update will cause array activity to be
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| 281 | suspended until the event is acknowledged.
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| 282 |
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| 283 | resync_start
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| 284 | The point at which resync should start. If no resync is needed,
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| 285 | this will be a very large number (or ``none`` since 2.6.30-rc1). At
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| 286 | array creation it will default to 0, though starting the array as
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| 287 | ``clean`` will set it much larger.
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| 288 |
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| 289 | new_dev
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| 290 | This file can be written but not read. The value written should
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| 291 | be a block device number as major:minor. e.g. 8:0
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| 292 | This will cause that device to be attached to the array, if it is
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| 293 | available. It will then appear at md/dev-XXX (depending on the
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| 294 | name of the device) and further configuration is then possible.
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| 295 |
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| 296 | safe_mode_delay
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| 297 | When an md array has seen no write requests for a certain period
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| 298 | of time, it will be marked as ``clean``. When another write
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| 299 | request arrives, the array is marked as ``dirty`` before the write
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| 300 | commences. This is known as ``safe_mode``.
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| 301 | The ``certain period`` is controlled by this file which stores the
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| 302 | period as a number of seconds. The default is 200msec (0.200).
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| 303 | Writing a value of 0 disables safemode.
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| 304 |
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| 305 | array_state
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| 306 | This file contains a single word which describes the current
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| 307 | state of the array. In many cases, the state can be set by
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| 308 | writing the word for the desired state, however some states
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| 309 | cannot be explicitly set, and some transitions are not allowed.
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| 310 |
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| 311 | Select/poll works on this file. All changes except between
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| 312 | Active_idle and active (which can be frequent and are not
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| 313 | very interesting) are notified. active->active_idle is
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| 314 | reported if the metadata is externally managed.
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| 315 |
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| 316 | clear
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| 317 | No devices, no size, no level
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| 318 |
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| 319 | Writing is equivalent to STOP_ARRAY ioctl
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| 320 |
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| 321 | inactive
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| 322 | May have some settings, but array is not active
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| 323 | all IO results in error
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| 324 |
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| 325 | When written, doesn't tear down array, but just stops it
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| 326 |
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| 327 | suspended (not supported yet)
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| 328 | All IO requests will block. The array can be reconfigured.
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| 329 |
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| 330 | Writing this, if accepted, will block until array is quiescent
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| 331 |
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| 332 | readonly
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| 333 | no resync can happen. no superblocks get written.
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| 334 |
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| 335 | Write requests fail
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| 336 |
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| 337 | read-auto
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| 338 | like readonly, but behaves like ``clean`` on a write request.
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| 339 |
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| 340 | clean
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| 341 | no pending writes, but otherwise active.
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| 342 |
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| 343 | When written to inactive array, starts without resync
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| 344 |
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| 345 | If a write request arrives then
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| 346 | if metadata is known, mark ``dirty`` and switch to ``active``.
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| 347 | if not known, block and switch to write-pending
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| 348 |
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| 349 | If written to an active array that has pending writes, then fails.
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| 350 | active
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| 351 | fully active: IO and resync can be happening.
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| 352 | When written to inactive array, starts with resync
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| 353 |
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| 354 | write-pending
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| 355 | clean, but writes are blocked waiting for ``active`` to be written.
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| 356 |
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| 357 | active-idle
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| 358 | like active, but no writes have been seen for a while (safe_mode_delay).
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| 359 |
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| 360 | consistency_policy
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| 361 | This indicates how the array maintains consistency in case of unexpected
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| 362 | shutdown. It can be:
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| 363 |
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| 364 | none
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| 365 | Array has no redundancy information, e.g. raid0, linear.
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| 366 |
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| 367 | resync
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| 368 | Full resync is performed and all redundancy is regenerated when the
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| 369 | array is started after unclean shutdown.
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| 370 |
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| 371 | bitmap
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| 372 | Resync assisted by a write-intent bitmap.
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| 373 |
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| 374 | journal
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| 375 | For raid4/5/6, journal device is used to log transactions and replay
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| 376 | after unclean shutdown.
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| 377 |
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| 378 | ppl
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| 379 | For raid5 only, Partial Parity Log is used to close the write hole and
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| 380 | eliminate resync.
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| 381 |
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| 382 | The accepted values when writing to this file are ``ppl`` and ``resync``,
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| 383 | used to enable and disable PPL.
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| 384 |
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| 385 | uuid
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| 386 | This indicates the UUID of the array in the following format:
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| 387 | xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
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| 388 |
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| 389 | bitmap_type
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| 390 | [RW] When read, this file will display the current and available
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| 391 | bitmap for this array. The currently active bitmap will be enclosed
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| 392 | in [] brackets. Writing an bitmap name or ID to this file will switch
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| 393 | control of this array to that new bitmap. Note that writing a new
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| 394 | bitmap for created array is forbidden.
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| 395 |
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| 396 | none
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| 397 | No bitmap
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| 398 | bitmap
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| 399 | The default internal bitmap
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| 400 | llbitmap
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| 401 | The lockless internal bitmap
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| 402 |
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| 403 | If bitmap_type is not none, then additional bitmap attributes bitmap/xxx or
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| 404 | llbitmap/xxx will be created after md device KOBJ_CHANGE event.
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| 405 |
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| 406 | If bitmap_type is bitmap, then the md device will also contain:
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| 407 |
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| 408 | bitmap/location
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| 409 | This indicates where the write-intent bitmap for the array is
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| 410 | stored.
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| 411 |
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| 412 | It can be one of ``none``, ``file`` or ``[+-]N``.
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| 413 | ``file`` may later be extended to ``file:/file/name``
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| 414 | ``[+-]N`` means that many sectors from the start of the metadata.
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| 415 |
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| 416 | This is replicated on all devices. For arrays with externally
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| 417 | managed metadata, the offset is from the beginning of the
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| 418 | device.
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| 419 |
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| 420 | bitmap/chunksize
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| 421 | The size, in bytes, of the chunk which will be represented by a
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| 422 | single bit. For RAID456, it is a portion of an individual
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| 423 | device. For RAID10, it is a portion of the array. For RAID1, it
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| 424 | is both (they come to the same thing).
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| 425 |
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| 426 | bitmap/time_base
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| 427 | The time, in seconds, between looking for bits in the bitmap to
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| 428 | be cleared. In the current implementation, a bit will be cleared
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| 429 | between 2 and 3 times ``time_base`` after all the covered blocks
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| 430 | are known to be in-sync.
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| 431 |
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| 432 | bitmap/backlog
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| 433 | When write-mostly devices are active in a RAID1, write requests
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| 434 | to those devices proceed in the background - the filesystem (or
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| 435 | other user of the device) does not have to wait for them.
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| 436 | ``backlog`` sets a limit on the number of concurrent background
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| 437 | writes. If there are more than this, new writes will by
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| 438 | synchronous.
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| 439 |
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| 440 | bitmap/metadata
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| 441 | This can be either ``internal`` or ``external``.
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| 442 |
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| 443 | ``internal``
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| 444 | is the default and means the metadata for the bitmap
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| 445 | is stored in the first 256 bytes of the allocated space and is
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| 446 | managed by the md module.
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| 447 |
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| 448 | ``external``
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| 449 | means that bitmap metadata is managed externally to
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| 450 | the kernel (i.e. by some userspace program)
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| 451 |
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| 452 | bitmap/can_clear
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| 453 | This is either ``true`` or ``false``. If ``true``, then bits in the
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| 454 | bitmap will be cleared when the corresponding blocks are thought
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| 455 | to be in-sync. If ``false``, bits will never be cleared.
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| 456 | This is automatically set to ``false`` if a write happens on a
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| 457 | degraded array, or if the array becomes degraded during a write.
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| 458 | When metadata is managed externally, it should be set to true
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| 459 | once the array becomes non-degraded, and this fact has been
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| 460 | recorded in the metadata.
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| 461 |
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| 462 | If bitmap_type is llbitmap, then the md device will also contain:
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| 463 |
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| 464 | llbitmap/bits
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| 465 | This is read-only, show status of bitmap bits, the number of each
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| 466 | value.
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| 467 |
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| 468 | llbitmap/metadata
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| 469 | This is read-only, show bitmap metadata, include chunksize, chunkshift,
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| 470 | chunks, offset and daemon_sleep.
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| 471 |
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| 472 | llbitmap/daemon_sleep
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| 473 | This is read-write, time in seconds that daemon function will be
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| 474 | triggered to clear dirty bits.
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| 475 |
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| 476 | llbitmap/barrier_idle
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| 477 | This is read-write, time in seconds that page barrier will be idled,
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| 478 | means dirty bits in the page will be cleared.
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| 479 |
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| 480 | As component devices are added to an md array, they appear in the ``md``
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| 481 | directory as new directories named::
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| 482 |
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| 483 | dev-XXX
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| 484 |
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| 485 | where ``XXX`` is a name that the kernel knows for the device, e.g. hdb1.
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| 486 | Each directory contains:
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| 487 |
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| 488 | block
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| 489 | a symlink to the block device in /sys/block, e.g.::
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| 490 |
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| 491 | /sys/block/md0/md/dev-hdb1/block -> ../../../../block/hdb/hdb1
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| 492 |
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| 493 | super
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| 494 | A file containing an image of the superblock read from, or
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| 495 | written to, that device.
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| 496 |
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| 497 | state
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| 498 | A file recording the current state of the device in the array
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| 499 | which can be a comma separated list of:
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| 500 |
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| 501 | faulty
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| 502 | device has been kicked from active use due to
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| 503 | a detected fault, or it has unacknowledged bad
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| 504 | blocks
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| 505 |
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| 506 | in_sync
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| 507 | device is a fully in-sync member of the array
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| 508 |
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| 509 | writemostly
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| 510 | device will only be subject to read
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| 511 | requests if there are no other options.
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| 512 |
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| 513 | This applies only to raid1 arrays.
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| 514 |
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| 515 | blocked
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| 516 | device has failed, and the failure hasn't been
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| 517 | acknowledged yet by the metadata handler.
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| 518 |
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| 519 | Writes that would write to this device if
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| 520 | it were not faulty are blocked.
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| 521 |
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| 522 | spare
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| 523 | device is working, but not a full member.
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| 524 |
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| 525 | This includes spares that are in the process
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| 526 | of being recovered to
|
| 527 |
|
| 528 | write_error
|
| 529 | device has ever seen a write error.
|
| 530 |
|
| 531 | want_replacement
|
| 532 | device is (mostly) working but probably
|
| 533 | should be replaced, either due to errors or
|
| 534 | due to user request.
|
| 535 |
|
| 536 | replacement
|
| 537 | device is a replacement for another active
|
| 538 | device with same raid_disk.
|
| 539 |
|
| 540 |
|
| 541 | This list may grow in future.
|
| 542 |
|
| 543 | This can be written to.
|
| 544 |
|
| 545 | Writing ``faulty`` simulates a failure on the device.
|
| 546 |
|
| 547 | Writing ``remove`` removes the device from the array.
|
| 548 |
|
| 549 | Writing ``writemostly`` sets the writemostly flag.
|
| 550 |
|
| 551 | Writing ``-writemostly`` clears the writemostly flag.
|
| 552 |
|
| 553 | Writing ``blocked`` sets the ``blocked`` flag.
|
| 554 |
|
| 555 | Writing ``-blocked`` clears the ``blocked`` flags and allows writes
|
| 556 | to complete and possibly simulates an error.
|
| 557 |
|
| 558 | Writing ``in_sync`` sets the in_sync flag.
|
| 559 |
|
| 560 | Writing ``write_error`` sets writeerrorseen flag.
|
| 561 |
|
| 562 | Writing ``-write_error`` clears writeerrorseen flag.
|
| 563 |
|
| 564 | Writing ``want_replacement`` is allowed at any time except to a
|
| 565 | replacement device or a spare. It sets the flag.
|
| 566 |
|
| 567 | Writing ``-want_replacement`` is allowed at any time. It clears
|
| 568 | the flag.
|
| 569 |
|
| 570 | Writing ``replacement`` or ``-replacement`` is only allowed before
|
| 571 | starting the array. It sets or clears the flag.
|
| 572 |
|
| 573 |
|
| 574 | This file responds to select/poll. Any change to ``faulty``
|
| 575 | or ``blocked`` causes an event.
|
| 576 |
|
| 577 | errors
|
| 578 | An approximate count of read errors that have been detected on
|
| 579 | this device but have not caused the device to be evicted from
|
| 580 | the array (either because they were corrected or because they
|
| 581 | happened while the array was read-only). When using version-1
|
| 582 | metadata, this value persists across restarts of the array.
|
| 583 |
|
| 584 | This value can be written while assembling an array thus
|
| 585 | providing an ongoing count for arrays with metadata managed by
|
| 586 | userspace.
|
| 587 |
|
| 588 | slot
|
| 589 | This gives the role that the device has in the array. It will
|
| 590 | either be ``none`` if the device is not active in the array
|
| 591 | (i.e. is a spare or has failed) or an integer less than the
|
| 592 | ``raid_disks`` number for the array indicating which position
|
| 593 | it currently fills. This can only be set while assembling an
|
| 594 | array. A device for which this is set is assumed to be working.
|
| 595 |
|
| 596 | offset
|
| 597 | This gives the location in the device (in sectors from the
|
| 598 | start) where data from the array will be stored. Any part of
|
| 599 | the device before this offset is not touched, unless it is
|
| 600 | used for storing metadata (Formats 1.1 and 1.2).
|
| 601 |
|
| 602 | size
|
| 603 | The amount of the device, after the offset, that can be used
|
| 604 | for storage of data. This will normally be the same as the
|
| 605 | component_size. This can be written while assembling an
|
| 606 | array. If a value less than the current component_size is
|
| 607 | written, it will be rejected.
|
| 608 |
|
| 609 | recovery_start
|
| 610 | When the device is not ``in_sync``, this records the number of
|
| 611 | sectors from the start of the device which are known to be
|
| 612 | correct. This is normally zero, but during a recovery
|
| 613 | operation it will steadily increase, and if the recovery is
|
| 614 | interrupted, restoring this value can cause recovery to
|
| 615 | avoid repeating the earlier blocks. With v1.x metadata, this
|
| 616 | value is saved and restored automatically.
|
| 617 |
|
| 618 | This can be set whenever the device is not an active member of
|
| 619 | the array, either before the array is activated, or before
|
| 620 | the ``slot`` is set.
|
| 621 |
|
| 622 | Setting this to ``none`` is equivalent to setting ``in_sync``.
|
| 623 | Setting to any other value also clears the ``in_sync`` flag.
|
| 624 |
|
| 625 | bad_blocks
|
| 626 | This gives the list of all known bad blocks in the form of
|
| 627 | start address and length (in sectors respectively). If output
|
| 628 | is too big to fit in a page, it will be truncated. Writing
|
| 629 | ``sector length`` to this file adds new acknowledged (i.e.
|
| 630 | recorded to disk safely) bad blocks.
|
| 631 |
|
| 632 | unacknowledged_bad_blocks
|
| 633 | This gives the list of known-but-not-yet-saved-to-disk bad
|
| 634 | blocks in the same form of ``bad_blocks``. If output is too big
|
| 635 | to fit in a page, it will be truncated. Writing to this file
|
| 636 | adds bad blocks without acknowledging them. This is largely
|
| 637 | for testing.
|
| 638 |
|
| 639 | ppl_sector, ppl_size
|
| 640 | Location and size (in sectors) of the space used for Partial Parity Log
|
| 641 | on this device.
|
| 642 |
|
| 643 |
|
| 644 | An active md device will also contain an entry for each active device
|
| 645 | in the array. These are named::
|
| 646 |
|
| 647 | rdNN
|
| 648 |
|
| 649 | where ``NN`` is the position in the array, starting from 0.
|
| 650 | So for a 3 drive array there will be rd0, rd1, rd2.
|
| 651 | These are symbolic links to the appropriate ``dev-XXX`` entry.
|
| 652 | Thus, for example::
|
| 653 |
|
| 654 | cat /sys/block/md*/md/rd*/state
|
| 655 |
|
| 656 | will show ``in_sync`` on every line.
|
| 657 |
|
| 658 |
|
| 659 |
|
| 660 | Active md devices for levels that support data redundancy (1,4,5,6,10)
|
| 661 | also have
|
| 662 |
|
| 663 | sync_action
|
| 664 | a text file that can be used to monitor and control the rebuild
|
| 665 | process. It contains one word which can be one of:
|
| 666 |
|
| 667 | resync
|
| 668 | redundancy is being recalculated after unclean
|
| 669 | shutdown or creation
|
| 670 |
|
| 671 | recover
|
| 672 | a hot spare is being built to replace a
|
| 673 | failed/missing device
|
| 674 |
|
| 675 | idle
|
| 676 | nothing is happening
|
| 677 | check
|
| 678 | A full check of redundancy was requested and is
|
| 679 | happening. This reads all blocks and checks
|
| 680 | them. A repair may also happen for some raid
|
| 681 | levels.
|
| 682 |
|
| 683 | repair
|
| 684 | A full check and repair is happening. This is
|
| 685 | similar to ``resync``, but was requested by the
|
| 686 | user, and the write-intent bitmap is NOT used to
|
| 687 | optimise the process.
|
| 688 |
|
| 689 | This file is writable, and each of the strings that could be
|
| 690 | read are meaningful for writing.
|
| 691 |
|
| 692 | ``idle`` will stop an active resync/recovery etc. There is no
|
| 693 | guarantee that another resync/recovery may not be automatically
|
| 694 | started again, though some event will be needed to trigger
|
| 695 | this.
|
| 696 |
|
| 697 | ``resync`` or ``recovery`` can be used to restart the
|
| 698 | corresponding operation if it was stopped with ``idle``.
|
| 699 |
|
| 700 | ``check`` and ``repair`` will start the appropriate process
|
| 701 | providing the current state is ``idle``.
|
| 702 |
|
| 703 | This file responds to select/poll. Any important change in the value
|
| 704 | triggers a poll event. Sometimes the value will briefly be
|
| 705 | ``recover`` if a recovery seems to be needed, but cannot be
|
| 706 | achieved. In that case, the transition to ``recover`` isn't
|
| 707 | notified, but the transition away is.
|
| 708 |
|
| 709 | degraded
|
| 710 | This contains a count of the number of devices by which the
|
| 711 | arrays is degraded. So an optimal array will show ``0``. A
|
| 712 | single failed/missing drive will show ``1``, etc.
|
| 713 |
|
| 714 | This file responds to select/poll, any increase or decrease
|
| 715 | in the count of missing devices will trigger an event.
|
| 716 |
|
| 717 | mismatch_count
|
| 718 | When performing ``check`` and ``repair``, and possibly when
|
| 719 | performing ``resync``, md will count the number of errors that are
|
| 720 | found. The count in ``mismatch_cnt`` is the number of sectors
|
| 721 | that were re-written, or (for ``check``) would have been
|
| 722 | re-written. As most raid levels work in units of pages rather
|
| 723 | than sectors, this may be larger than the number of actual errors
|
| 724 | by a factor of the number of sectors in a page.
|
| 725 |
|
| 726 | bitmap_set_bits
|
| 727 | If the array has a write-intent bitmap, then writing to this
|
| 728 | attribute can set bits in the bitmap, indicating that a resync
|
| 729 | would need to check the corresponding blocks. Either individual
|
| 730 | numbers or start-end pairs can be written. Multiple numbers
|
| 731 | can be separated by a space.
|
| 732 |
|
| 733 | Note that the numbers are ``bit`` numbers, not ``block`` numbers.
|
| 734 | They should be scaled by the bitmap_chunksize.
|
| 735 |
|
| 736 | sync_speed_min, sync_speed_max
|
| 737 | These are similar to ``/proc/sys/dev/raid/speed_limit_{min,max}``
|
| 738 | however they only apply to the particular array.
|
| 739 |
|
| 740 | If no value has been written to these, or if the word ``system``
|
| 741 | is written, then the system-wide value is used. If a value,
|
| 742 | in kibibytes-per-second is written, then it is used.
|
| 743 |
|
| 744 | When the files are read, they show the currently active value
|
| 745 | followed by ``(local)`` or ``(system)`` depending on whether it is
|
| 746 | a locally set or system-wide value.
|
| 747 |
|
| 748 | sync_completed
|
| 749 | This shows the number of sectors that have been completed of
|
| 750 | whatever the current sync_action is, followed by the number of
|
| 751 | sectors in total that could need to be processed. The two
|
| 752 | numbers are separated by a ``/`` thus effectively showing one
|
| 753 | value, a fraction of the process that is complete.
|
| 754 |
|
| 755 | A ``select`` on this attribute will return when resync completes,
|
| 756 | when it reaches the current sync_max (below) and possibly at
|
| 757 | other times.
|
| 758 |
|
| 759 | sync_speed
|
| 760 | This shows the current actual speed, in K/sec, of the current
|
| 761 | sync_action. It is averaged over the last 30 seconds.
|
| 762 |
|
| 763 | suspend_lo, suspend_hi
|
| 764 | The two values, given as numbers of sectors, indicate a range
|
| 765 | within the array where IO will be blocked. This is currently
|
| 766 | only supported for raid4/5/6.
|
| 767 |
|
| 768 | sync_min, sync_max
|
| 769 | The two values, given as numbers of sectors, indicate a range
|
| 770 | within the array where ``check``/``repair`` will operate. Must be
|
| 771 | a multiple of chunk_size. When it reaches ``sync_max`` it will
|
| 772 | pause, rather than complete.
|
| 773 | You can use ``select`` or ``poll`` on ``sync_completed`` to wait for
|
| 774 | that number to reach sync_max. Then you can either increase
|
| 775 | ``sync_max``, or can write ``idle`` to ``sync_action``.
|
| 776 |
|
| 777 | The value of ``max`` for ``sync_max`` effectively disables the limit.
|
| 778 | When a resync is active, the value can only ever be increased,
|
| 779 | never decreased.
|
| 780 | The value of ``0`` is the minimum for ``sync_min``.
|
| 781 |
|
| 782 |
|
| 783 |
|
| 784 | Each active md device may also have attributes specific to the
|
| 785 | personality module that manages it.
|
| 786 | These are specific to the implementation of the module and could
|
| 787 | change substantially if the implementation changes.
|
| 788 |
|
| 789 | These currently include:
|
| 790 |
|
| 791 | stripe_cache_size (currently raid5 only)
|
| 792 | number of entries in the stripe cache. This is writable, but
|
| 793 | there are upper and lower limits (32768, 17). Default is 256.
|
| 794 |
|
| 795 | strip_cache_active (currently raid5 only)
|
| 796 | number of active entries in the stripe cache
|
| 797 |
|
| 798 | preread_bypass_threshold (currently raid5 only)
|
| 799 | number of times a stripe requiring preread will be bypassed by
|
| 800 | a stripe that does not require preread. For fairness defaults
|
| 801 | to 1. Setting this to 0 disables bypass accounting and
|
| 802 | requires preread stripes to wait until all full-width stripe-
|
| 803 | writes are complete. Valid values are 0 to stripe_cache_size.
|
| 804 |
|
| 805 | journal_mode (currently raid5 only)
|
| 806 | The cache mode for raid5. raid5 could include an extra disk for
|
| 807 | caching. The mode can be "write-through" or "write-back". The
|
| 808 | default is "write-through".
|
| 809 |
|
| 810 | ppl_write_hint
|
| 811 | NVMe stream ID to be set for each PPL write request.
|