119 lines
4 KiB
Text
119 lines
4 KiB
Text
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Tools that manage md devices can be found at
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http://www.<country>.kernel.org/pub/linux/utils/raid/....
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Boot time assembly of RAID arrays
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---------------------------------
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You can boot with your md device with the following kernel command
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lines:
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for old raid arrays without persistent superblocks:
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md=<md device no.>,<raid level>,<chunk size factor>,<fault level>,dev0,dev1,...,devn
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for raid arrays with persistent superblocks
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md=<md device no.>,dev0,dev1,...,devn
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or, to assemble a partitionable array:
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md=d<md device no.>,dev0,dev1,...,devn
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md device no. = the number of the md device ...
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0 means md0,
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1 md1,
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2 md2,
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3 md3,
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4 md4
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raid level = -1 linear mode
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0 striped mode
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other modes are only supported with persistent super blocks
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chunk size factor = (raid-0 and raid-1 only)
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Set the chunk size as 4k << n.
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fault level = totally ignored
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dev0-devn: e.g. /dev/hda1,/dev/hdc1,/dev/sda1,/dev/sdb1
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A possible loadlin line (Harald Hoyer <HarryH@Royal.Net>) looks like this:
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e:\loadlin\loadlin e:\zimage root=/dev/md0 md=0,0,4,0,/dev/hdb2,/dev/hdc3 ro
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Boot time autodetection of RAID arrays
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--------------------------------------
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When md is compiled into the kernel (not as module), partitions of
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type 0xfd are scanned and automatically assembled into RAID arrays.
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This autodetection may be suppressed with the kernel parameter
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"raid=noautodetect". As of kernel 2.6.9, only drives with a type 0
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superblock can be autodetected and run at boot time.
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The kernel parameter "raid=partitionable" (or "raid=part") means
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that all auto-detected arrays are assembled as partitionable.
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Superblock formats
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------------------
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The md driver can support a variety of different superblock formats.
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Currently, it supports superblock formats "0.90.0" and the "md-1" format
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introduced in the 2.5 development series.
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The kernel will autodetect which format superblock is being used.
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Superblock format '0' is treated differently to others for legacy
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reasons - it is the original superblock format.
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General Rules - apply for all superblock formats
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------------------------------------------------
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An array is 'created' by writing appropriate superblocks to all
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devices.
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It is 'assembled' by associating each of these devices with an
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particular md virtual device. Once it is completely assembled, it can
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be accessed.
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An array should be created by a user-space tool. This will write
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superblocks to all devices. It will usually mark the array as
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'unclean', or with some devices missing so that the kernel md driver
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can create appropriate redundancy (copying in raid1, parity
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calculation in raid4/5).
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When an array is assembled, it is first initialized with the
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SET_ARRAY_INFO ioctl. This contains, in particular, a major and minor
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version number. The major version number selects which superblock
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format is to be used. The minor number might be used to tune handling
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of the format, such as suggesting where on each device to look for the
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superblock.
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Then each device is added using the ADD_NEW_DISK ioctl. This
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provides, in particular, a major and minor number identifying the
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device to add.
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The array is started with the RUN_ARRAY ioctl.
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Once started, new devices can be added. They should have an
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appropriate superblock written to them, and then passed be in with
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ADD_NEW_DISK.
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Devices that have failed or are not yet active can be detached from an
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array using HOT_REMOVE_DISK.
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Specific Rules that apply to format-0 super block arrays, and
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arrays with no superblock (non-persistent).
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-------------------------------------------------------------
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An array can be 'created' by describing the array (level, chunksize
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etc) in a SET_ARRAY_INFO ioctl. This must has major_version==0 and
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raid_disks != 0.
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Then uninitialized devices can be added with ADD_NEW_DISK. The
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structure passed to ADD_NEW_DISK must specify the state of the device
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and it's role in the array.
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Once started with RUN_ARRAY, uninitialized spares can be added with
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HOT_ADD_DISK.
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