minor typo fixes in md.txt
From: Christian Kujau
Date: Mon Jul 31 2006 - 07:59:42 EST
Hi,
I stumbled over a double occurrence of the "level" file explained, so
I took the opportunity and played Mr. Nitpick for this file. Hope you don't
mind...
Signed-off-by: Christian Kujau <evil@xxxxxxxxxx>
Thanks,
Christian.
--
BOFH excuse #230:
Lusers learning curve appears to be fractal--- linux-2.6/Documentation/md.txt.orig 2006-07-31 02:45:25.000000000 +0100
+++ linux-2.6/Documentation/md.txt 2006-07-31 03:01:52.000000000 +0100
@@ -29,11 +29,11 @@
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@xxxxxxxxx>) looks like this:
e:\loadlin\loadlin e:\zimage root=/dev/md0 md=0,0,4,0,/dev/hdb2,/dev/hdc3 ro
@@ -45,7 +45,7 @@
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
+"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
@@ -55,18 +55,18 @@
-------------------------------------------
If a raid5 or raid6 array is both dirty and degraded, it could have
-undetectable data corruption. This is because the fact that it is
+undetectable data corruption. This is because the fact that it is
'dirty' means that the parity cannot be trusted, and the fact that it
is degraded means that some datablocks are missing and cannot reliably
be reconstructed (due to no parity).
-For this reason, md will normally refuse to start such an array. This
+For this reason, md will normally refuse to start such an array. This
requires the sysadmin to take action to explicitly start the array
-desipite possible corruption. This is normally done with
+desipite possible corruption. This is normally done with
mdadm --assemble --force ....
This option is not really available if the array has the root
-filesystem on it. In order to support this booting from such an
+filesystem on it. In order to support this booting from such an
array, md supports a module parameter "start_dirty_degraded" which,
when set to 1, bypassed the checks and will allows dirty degraded
arrays to be started.
@@ -96,29 +96,29 @@
devices.
It is 'assembled' by associating each of these devices with an
-particular md virtual device. Once it is completely assembled, it can
+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
+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
+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
+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
+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.
@@ -127,14 +127,14 @@
Specific Rules that apply to format-0 super block arrays, and
- arrays with no superblock (non-persistent).
+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
+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
+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.
@@ -154,19 +154,21 @@
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
+ a text file indicating the 'raid level'. This may be a standard
+ numerical level prefixed by "raid" - e.g. "raid5", 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.
+ This can be written only while the array is being assembled, not
+ after it is started.
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
+ 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.
Some raid level (RAID1) allow this value to be set while the
- array is active. This will reconfigure the array. Otherwise
+ array is active. This will reconfigure the array. Otherwise
it can only be set while assembling an array.
chunk_size
@@ -181,55 +183,47 @@
For arrays with data redundancy (i.e. not raid0, linear, faulty,
multipath), all components must be the same size - or at least
there must a size that they all provide space for. This is a key
- part or the geometry of the array. It is measured in sectors
- and can be read from here. Writing to this value may resize
+ part or the geometry of the array. It is measured in sectors
+ and can be read from here. Writing to this value may resize
the array if the personality supports it (raid1, raid5, raid6),
and if the component drives are large enough.
metadata_version
This indicates the format that is being used to record metadata
- about the array. It can be 0.90 (traditional format), 1.0, 1.1,
+ about the array. It can be 0.90 (traditional format), 1.0, 1.1,
1.2 (newer format in varying locations) or "none" indicating that
the kernel isn't managing metadata at all.
- level
- The raid 'level' for this array. The name will often (but not
- always) be the same as the name of the module that implements the
- level. To be auto-loaded the module must have an alias
- md-$LEVEL e.g. md-raid5
- This can be written only while the array is being assembled, not
- after it is started.
-
layout
- The "layout" for the array for the particular level. This is
+ The "layout" for the array for the particular level. This is
simply a number that is interpretted differently by different
- levels. It can be written while assembling an array.
+ levels. It can be written while assembling an array.
resync_start
- The point at which resync should start. If no resync is needed,
- this will be a very large number. At array creation it will
+ The point at which resync should start. If no resync is needed,
+ this will be a very large number. At array creation it will
default to 0, though starting the array as 'clean' will
set it much larger.
new_dev
- This file can be written but not read. The value written should
- be a block device number as major:minor. e.g. 8:0
+ This file can be written but not read. The value written should
+ be a block device number as major:minor, e.g. 8:0.
This will cause that device to be attached to the array, if it is
- available. It will then appear at md/dev-XXX (depending on the
+ available. It will then appear at md/dev-XXX (depending on the
name of the device) and further configuration is then possible.
safe_mode_delay
When an md array has seen no write requests for a certain period
- of time, it will be marked as 'clean'. When another write
+ of time, it will be marked as 'clean'. When another write
request arrive, the array is marked as 'dirty' before the write
- commenses. This is known as 'safe_mode'.
+ commenses. This is known as 'safe_mode'.
The 'certain period' is controlled by this file which stores the
- period as a number of seconds. The default is 200msec (0.200).
+ period as a number of seconds. The default is 200msec (0.200).
Writing a value of 0 disables safemode.
array_state
This file contains a single word which describes the current
- state of the array. In many cases, the state can be set by
+ state of the array. In many cases, the state can be set by
writing the word for the desired state, however some states
cannot be explicitly set, and some transitions are not allowed.
@@ -242,10 +236,12 @@
When written, doesn't tear down array, but just stops it
suspended (not supported yet)
All IO requests will block. The array can be reconfigured.
- Writing this, if accepted, will block until array is quiessent
+ Writing this, if accepted, will block until array is quiescent.
+
readonly
- no resync can happen. no superblocks get written.
+ no resync can happen. no superblocks get written.
write requests fail
+
read-auto
like readonly, but behaves like 'clean' on a write request.
@@ -255,6 +251,7 @@
if metadata is known, mark 'dirty' and switch to 'active'.
if not known, block and switch to write-pending
If written to an active array that has pending writes, then fails.
+
active
fully active: IO and resync can be happening.
When written to inactive array, starts with resync
@@ -271,7 +268,7 @@
This are similar to /proc/sys/dev/raid/speed_limit_{min,max}
however they only apply to the particular array.
If no value has been written to these, of if the word 'system'
- is written, then the system-wide value is used. If a value,
+ is written, then the system-wide value is used. If a value,
in kibibytes-per-second is written, then it is used.
When the files are read, they show the currently active value
followed by "(local)" or "(system)" depending on whether it is
@@ -280,13 +277,13 @@
sync_completed
This shows the number of sectors that have been completed of
whatever the current sync_action is, followed by the number of
- sectors in total that could need to be processed. The two
- numbers are separated by a '/' thus effectively showing one
+ sectors in total that could need to be processed. The two
+ numbers are separated by a '/' thus effectively showing one
value, a fraction of the process that is complete.
sync_speed
This shows the current actual speed, in K/sec, of the current
- sync_action. It is averaged over the last 30 seconds.
+ sync_action. It is averaged over the last 30 seconds.
As component devices are added to an md array, they appear in the 'md'
@@ -326,7 +323,7 @@
An approximate count of read errors that have been detected on
this device but have not caused the device to be evicted from
the array (either because they were corrected or because they
- happened while the array was read-only). When using version-1
+ happened while the array was read-only). When using version-1
metadata, this value persists across restarts of the array.
This value can be written while assembling an array thus
@@ -334,29 +331,29 @@
userspace.
slot
- This gives the role that the device has in the array. It will
+ This gives the role that the device has in the array. It will
either be 'none' if the device is not active in the array
(i.e. is a spare or has failed) or an integer less than the
'raid_disks' number for the array indicating which possition
- it currently fills. This can only be set while assembling an
- array. A device for which this is set is assumed to be working.
+ it currently fills. This can only be set while assembling an
+ array. A device for which this is set is assumed to be working.
offset
This gives the location in the device (in sectors from the
- start) where data from the array will be stored. Any part of
+ start) where data from the array will be stored. Any part of
the device before this offset us not touched, unless it is
used for storing metadata (Formats 1.1 and 1.2).
size
The amount of the device, after the offset, that can be used
- for storage of data. This will normally be the same as the
- component_size. This can be written while assembling an
- array. If a value less than the current component_size is
+ for storage of data. This will normally be the same as the
+ component_size. This can be written while assembling an
+ array. If a value less than the current component_size is
written, component_size will be reduced to this value.
An active md device will also contain and entry for each active device
-in the array. These are named
+in the array. These are named
rdNN
@@ -368,23 +365,22 @@
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:
+ 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
+ happening. This reads all blocks and checks
them. A repair may also happen for some raid
levels.
- repair - A full check and repair is happening. This is
+ 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.
@@ -392,7 +388,7 @@
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
+ '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.
@@ -404,9 +400,9 @@
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
+ 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
+ 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.