Documentation/md.txt

Tools that manage md devices can be found at
   http://www.<country>.kernel.org/pub/linux/utils/raid/....



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
  
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

-------------------------------
The md driver can support a variety of different superblock formats.
(It doesn't yet, but it can)

The kernel does *NOT* autodetect which format superblock is being
used. It must be told.

Superblock format '0' is treated differently to others for legacy
reasons.


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 approrpriate redundancy (copying in raid1, parity
calculation in raid4/5).

When an array is assembled, it is first initialised 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-presistant).
-------------------------------------------------------------

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 uninitialised 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.

One started with RUN_ARRAY, uninitialised spares can be added with
HOT_ADD_DISK.