1 Tools that manage md devices can be found at
2 http://www.<country>.kernel.org/pub/linux/utils/raid/....
5 Boot time assembly of RAID arrays
6 ---------------------------------
8 You can boot with your md device with the following kernel command
11 for old raid arrays without persistent superblocks:
12 md=<md device no.>,<raid level>,<chunk size factor>,<fault level>,dev0,dev1,...,devn
14 for raid arrays with persistent superblocks
15 md=<md device no.>,dev0,dev1,...,devn
16 or, to assemble a partitionable array:
17 md=d<md device no.>,dev0,dev1,...,devn
19 md device no. = the number of the md device ...
26 raid level = -1 linear mode
28 other modes are only supported with persistent super blocks
30 chunk size factor = (raid-0 and raid-1 only)
31 Set the chunk size as 4k << n.
33 fault level = totally ignored
35 dev0-devn: e.g. /dev/hda1,/dev/hdc1,/dev/sda1,/dev/sdb1
37 A possible loadlin line (Harald Hoyer <HarryH@Royal.Net>) looks like this:
39 e:\loadlin\loadlin e:\zimage root=/dev/md0 md=0,0,4,0,/dev/hdb2,/dev/hdc3 ro
42 Boot time autodetection of RAID arrays
43 --------------------------------------
45 When md is compiled into the kernel (not as module), partitions of
46 type 0xfd are scanned and automatically assembled into RAID arrays.
47 This autodetection may be suppressed with the kernel parameter
50 The kernel parameter "raid=partitionable" (or "raid=part") means
51 that all auto-detected arrays are assembled as partitionable.
57 The md driver can support a variety of different superblock formats.
58 (It doesn't yet, but it can)
60 The kernel does *NOT* autodetect which format superblock is being
61 used. It must be told.
63 Superblock format '0' is treated differently to others for legacy
67 General Rules - apply for all superblock formats
68 ------------------------------------------------
70 An array is 'created' by writing appropriate superblocks to all
72 It is 'assembled' by associating each of these devices with an
73 particular md virtual device. Once it is completely assembled, it can
76 An array should be created by a user-space tool. This will write
77 superblocks to all devices. It will usually mark the array as
78 'unclean', or with some devices missing so that the kernel md driver
79 can create approrpriate redundancy (copying in raid1, parity
80 calculation in raid4/5).
82 When an array is assembled, it is first initialised with the
83 SET_ARRAY_INFO ioctl. This contains, in particular, a major and minor
84 version number. The major version number selects which superblock
85 format is to be used. The minor number might be used to tune handling
86 of the format, such as suggesting where on each device to look for the
89 Then each device is added using the ADD_NEW_DISK ioctl. This
90 provides, in particular, a major and minor number identifying the
93 The array is started with the RUN_ARRAY ioctl.
95 Once started, new devices can be added. They should have an
96 appropriate superblock written to them, and then passed be in with
99 Devices that have failed or are not yet active can be detached from an
100 array using HOT_REMOVE_DISK.
103 Specific Rules that apply to format-0 super block arrays, and
104 arrays with no superblock (non-persistant).
105 -------------------------------------------------------------
107 An array can be 'created' by describing the array (level, chunksize
108 etc) in a SET_ARRAY_INFO ioctl. This must has major_version==0 and
110 Then uninitialised devices can be added with ADD_NEW_DISK. The
111 structure passed to ADD_NEW_DISK must specify the state of the device
112 and it's role in the array.
114 One started with RUN_ARRAY, uninitialised spares can be added with