Commit 2a9e1b61 authored by James Nelson's avatar James Nelson Committed by Linus Torvalds

[PATCH] md: Documentation/md.txt update

Updates to Documentation/md.txt - included some extra info I found out
while digging deeper into init/do_mounts_md.c
Signed-off-by: default avatarJames Nelson <James4765@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent f5711563
......@@ -45,7 +45,8 @@ 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".
"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.
......@@ -55,13 +56,13 @@ Superblock formats
------------------
The md driver can support a variety of different superblock formats.
(It doesn't yet, but it can)
Currently, it supports superblock formats "0.90.0" and the "md-1" format
introduced in the 2.5 development series.
The kernel does *NOT* autodetect which format superblock is being
used. It must be told.
The kernel will autodetect which format superblock is being used.
Superblock format '0' is treated differently to others for legacy
reasons.
reasons - it is the original superblock format.
General Rules - apply for all superblock formats
......@@ -69,6 +70,7 @@ 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.
......@@ -76,10 +78,10 @@ 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
can create appropriate redundancy (copying in raid1, parity
calculation in raid4/5).
When an array is assembled, it is first initialised with the
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
......@@ -101,15 +103,16 @@ array using HOT_REMOVE_DISK.
Specific Rules that apply to format-0 super block arrays, and
arrays with no superblock (non-persistant).
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 uninitialised devices can be added with ADD_NEW_DISK. The
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.
One started with RUN_ARRAY, uninitialised spares can be added with
Once started with RUN_ARRAY, uninitialized spares can be added with
HOT_ADD_DISK.
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