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