You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
237 lines
8.6 KiB
237 lines
8.6 KiB
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.
|
|
|
|
|
|
|
|
MD devices in sysfs
|
|
-------------------
|
|
md devices appear in sysfs (/sys) as regular block devices,
|
|
e.g.
|
|
/sys/block/md0
|
|
|
|
Each 'md' device will contain a subdirectory called 'md' which
|
|
contains further md-specific information about the device.
|
|
|
|
All md devices contain:
|
|
level
|
|
a text file indicating the 'raid level'. This may be a standard
|
|
numerical level prefixed by "RAID-" - e.g. "RAID-5", or some
|
|
other name such as "linear" or "multipath".
|
|
If no raid level has been set yet (array is still being
|
|
assembled), this file will be empty.
|
|
|
|
raid_disks
|
|
a text file with a simple number indicating the number of devices
|
|
in a fully functional array. If this is not yet known, the file
|
|
will be empty. If an array is being resized (not currently
|
|
possible) this will contain the larger of the old and new sizes.
|
|
|
|
As component devices are added to an md array, they appear in the 'md'
|
|
directory as new directories named
|
|
dev-XXX
|
|
where XXX is a name that the kernel knows for the device, e.g. hdb1.
|
|
Each directory contains:
|
|
|
|
block
|
|
a symlink to the block device in /sys/block, e.g.
|
|
/sys/block/md0/md/dev-hdb1/block -> ../../../../block/hdb/hdb1
|
|
|
|
super
|
|
A file containing an image of the superblock read from, or
|
|
written to, that device.
|
|
|
|
state
|
|
A file recording the current state of the device in the array
|
|
which can be a comma separated list of
|
|
faulty - device has been kicked from active use due to
|
|
a detected fault
|
|
in_sync - device is a fully in-sync member of the array
|
|
spare - device is working, but not a full member.
|
|
This includes spares that are in the process
|
|
of being recoverred to
|
|
This list make grow in future.
|
|
|
|
|
|
An active md device will also contain and entry for each active device
|
|
in the array. These are named
|
|
|
|
rdNN
|
|
|
|
where 'NN' is the possition in the array, starting from 0.
|
|
So for a 3 drive array there will be rd0, rd1, rd2.
|
|
These are symbolic links to the appropriate 'dev-XXX' entry.
|
|
Thus, for example,
|
|
cat /sys/block/md*/md/rd*/state
|
|
will show 'in_sync' on every line.
|
|
|
|
|
|
|
|
Active md devices for levels that support data redundancy (1,4,5,6)
|
|
also have
|
|
|
|
sync_action
|
|
a text file that can be used to monitor and control the rebuild
|
|
process. It contains one word which can be one of:
|
|
resync - redundancy is being recalculated after unclean
|
|
shutdown or creation
|
|
recover - a hot spare is being built to replace a
|
|
failed/missing device
|
|
idle - nothing is happening
|
|
check - A full check of redundancy was requested and is
|
|
happening. This reads all block and checks
|
|
them. A repair may also happen for some raid
|
|
levels.
|
|
repair - A full check and repair is happening. This is
|
|
similar to 'resync', but was requested by the
|
|
user, and the write-intent bitmap is NOT used to
|
|
optimise the process.
|
|
|
|
This file is writable, and each of the strings that could be
|
|
read are meaningful for writing.
|
|
|
|
'idle' will stop an active resync/recovery etc. There is no
|
|
guarantee that another resync/recovery may not be automatically
|
|
started again, though some event will be needed to trigger
|
|
this.
|
|
'resync' or 'recovery' can be used to restart the
|
|
corresponding operation if it was stopped with 'idle'.
|
|
'check' and 'repair' will start the appropriate process
|
|
providing the current state is 'idle'.
|
|
|
|
mismatch_count
|
|
When performing 'check' and 'repair', and possibly when
|
|
performing 'resync', md will count the number of errors that are
|
|
found. The count in 'mismatch_cnt' is the number of sectors
|
|
that were re-written, or (for 'check') would have been
|
|
re-written. As most raid levels work in units of pages rather
|
|
than sectors, this my be larger than the number of actual errors
|
|
by a factor of the number of sectors in a page.
|
|
|
|
Each active md device may also have attributes specific to the
|
|
personality module that manages it.
|
|
These are specific to the implementation of the module and could
|
|
change substantially if the implementation changes.
|
|
|
|
These currently include
|
|
|
|
stripe_cache_size (currently raid5 only)
|
|
number of entries in the stripe cache. This is writable, but
|
|
there are upper and lower limits (32768, 16). Default is 128.
|
|
strip_cache_active (currently raid5 only)
|
|
number of active entries in the stripe cache
|
|
|