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diff --git a/Documentation/admin-guide/device-mapper/dm-ebs.rst b/Documentation/admin-guide/device-mapper/dm-ebs.rst new file mode 100644 index 000000000000..534fa38e8862 --- /dev/null +++ b/Documentation/admin-guide/device-mapper/dm-ebs.rst @@ -0,0 +1,51 @@ +====== +dm-ebs +====== + + +This target is similar to the linear target except that it emulates +a smaller logical block size on a device with a larger logical block +size. Its main purpose is to provide emulation of 512 byte sectors on +devices that do not provide this emulation (i.e. 4K native disks). + +Supported emulated logical block sizes 512, 1024, 2048 and 4096. + +Underlying block size can be set to > 4K to test buffering larger units. + + +Table parameters +---------------- + <dev path> <offset> <emulated sectors> [<underlying sectors>] + +Mandatory parameters: + + <dev path>: + Full pathname to the underlying block-device, + or a "major:minor" device-number. + <offset>: + Starting sector within the device; + has to be a multiple of <emulated sectors>. + <emulated sectors>: + Number of sectors defining the logical block size to be emulated; + 1, 2, 4, 8 sectors of 512 bytes supported. + +Optional parameter: + + <underyling sectors>: + Number of sectors defining the logical block size of <dev path>. + 2^N supported, e.g. 8 = emulate 8 sectors of 512 bytes = 4KiB. + If not provided, the logical block size of <dev path> will be used. + + +Examples: + +Emulate 1 sector = 512 bytes logical block size on /dev/sda starting at +offset 1024 sectors with underlying devices block size automatically set: + +ebs /dev/sda 1024 1 + +Emulate 2 sector = 1KiB logical block size on /dev/sda starting at +offset 128 sectors, enforce 2KiB underlying device block size. +This presumes 2KiB logical blocksize on /dev/sda or less to work: + +ebs /dev/sda 128 2 4 |