| 1 | ======
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| 2 | dm-ebs
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| 3 | ======
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| 4 |
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| 5 |
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| 6 | This target is similar to the linear target except that it emulates
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| 7 | a smaller logical block size on a device with a larger logical block
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| 8 | size. Its main purpose is to provide emulation of 512 byte sectors on
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| 9 | devices that do not provide this emulation (i.e. 4K native disks).
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| 10 |
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| 11 | Supported emulated logical block sizes 512, 1024, 2048 and 4096.
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| 12 |
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| 13 | Underlying block size can be set to > 4K to test buffering larger units.
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| 14 |
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| 15 |
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| 16 | Table parameters
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| 17 | ----------------
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| 18 | <dev path> <offset> <emulated sectors> [<underlying sectors>]
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| 19 |
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| 20 | Mandatory parameters:
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| 21 |
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| 22 | <dev path>:
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| 23 | Full pathname to the underlying block-device,
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| 24 | or a "major:minor" device-number.
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| 25 | <offset>:
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| 26 | Starting sector within the device;
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| 27 | has to be a multiple of <emulated sectors>.
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| 28 | <emulated sectors>:
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| 29 | Number of sectors defining the logical block size to be emulated;
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| 30 | 1, 2, 4, 8 sectors of 512 bytes supported.
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| 31 |
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| 32 | Optional parameter:
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| 33 |
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| 34 | <underlying sectors>:
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| 35 | Number of sectors defining the logical block size of <dev path>.
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| 36 | 2^N supported, e.g. 8 = emulate 8 sectors of 512 bytes = 4KiB.
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| 37 | If not provided, the logical block size of <dev path> will be used.
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| 38 |
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| 39 |
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| 40 | Examples:
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| 41 |
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| 42 | Emulate 1 sector = 512 bytes logical block size on /dev/sda starting at
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| 43 | offset 1024 sectors with underlying devices block size automatically set:
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| 44 |
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| 45 | ebs /dev/sda 1024 1
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| 46 |
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| 47 | Emulate 2 sector = 1KiB logical block size on /dev/sda starting at
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| 48 | offset 128 sectors, enforce 2KiB underlying device block size.
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| 49 | This presumes 2KiB logical blocksize on /dev/sda or less to work:
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| 50 |
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| 51 | ebs /dev/sda 128 2 4
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