fedora core 6 1.2949 + vserver 2.2.0

[linux-2.6.git] / Documentation / md.txt

diff --git a/Documentation/md.txt b/Documentation/md.txt
index 03a13c4..2202f5d 100644 (file)
--- a/Documentation/md.txt
+++ b/Documentation/md.txt
@@ -62,7 +62,7 @@ be reconstructed (due to no parity).
 
 For this reason, md will normally refuse to start such an array.  This
 requires the sysadmin to take action to explicitly start the array
 
 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
+despite possible corruption.  This is normally done with

    mdadm --assemble --force ....
 
 This option is not really available if the array has the root
    mdadm --assemble --force ....
 
 This option is not really available if the array has the root


@@ -154,11 +154,12 @@ contains further md-specific information about the device.
 
 All md devices contain:
   level
 
 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".
+     a text file indicating the 'raid level'. e.g. raid0, raid1,
+     raid5, linear, multipath, faulty.

      If no raid level has been set yet (array is still being
      If no raid level has been set yet (array is still being

-     assembled), this file will be empty.
+     assembled), the value will reflect whatever has been written
+     to it, which may be a name like the above, or may be a number
+     such as '0', '5', etc.

 
   raid_disks
      a text file with a simple number indicating the number of devices
 
   raid_disks
      a text file with a simple number indicating the number of devices


@@ -174,7 +175,7 @@ All md devices contain:
      raid levels that involve striping (1,4,5,6,10). The address space
      of the array is conceptually divided into chunks and consecutive
      chunks are striped onto neighbouring devices.
      raid levels that involve striping (1,4,5,6,10). The address space
      of the array is conceptually divided into chunks and consecutive
      chunks are striped onto neighbouring devices.

-     The size should be atleast PAGE_SIZE (4k) and should be a power
+     The size should be at least PAGE_SIZE (4k) and should be a power

      of 2.  This can only be set while assembling an array
 
   component_size
      of 2.  This can only be set while assembling an array
 
   component_size


@@ -192,13 +193,16 @@ All md devices contain:
      1.2 (newer format in varying locations) or "none" indicating that
      the kernel isn't managing metadata at all.
 
      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
+     simply a number that is interpretted differently by different
+     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
+     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
 
    new_dev
      This file can be written but not read.  The value written should


@@ -207,6 +211,54 @@ All md devices contain:
      available.  It will then appear at md/dev-XXX (depending on the
      name of the device) and further configuration is then possible.
 
      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
+     request arrives, the array is marked as 'dirty' before the write
+     commences.  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).
+     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
+     writing the word for the desired state, however some states
+     cannot be explicitly set, and some transitions are not allowed.
+
+     clear
+         No devices, no size, no level
+         Writing is equivalent to STOP_ARRAY ioctl
+     inactive
+         May have some settings, but array is not active
+            all IO results in error
+         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
+     readonly
+         no resync can happen.  no superblocks get written.
+         write requests fail
+     read-auto
+         like readonly, but behaves like 'clean' on a write request.
+
+     clean - no pending writes, but otherwise active.
+         When written to inactive array, starts without resync
+         If a write request arrives then
+           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
+
+     write-pending
+         clean, but writes are blocked waiting for 'active' to be written.
+
+     active-idle
+         like active, but no writes have been seen for a while (safe_mode_delay).
+
+

    sync_speed_min
    sync_speed_max
      This are similar to /proc/sys/dev/raid/speed_limit_{min,max}
    sync_speed_min
    sync_speed_max
      This are similar to /proc/sys/dev/raid/speed_limit_{min,max}


@@ -250,10 +302,18 @@ Each directory contains:
              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
              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

+             writemostly - device will only be subject to read
+                        requests if there are no other options.
+                        This applies only to raid1 arrays.

              spare    - device is working, but not a full member.
                         This includes spares that are in the process
              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.
+                        of being recovered to
+       This list may grow in future.
+       This can be written to.
+       Writing "faulty"  simulates a failure on the device.
+       Writing "remove" removes the device from the array.
+       Writing "writemostly" sets the writemostly flag.
+       Writing "-writemostly" clears the writemostly flag.

 
       errors
        An approximate count of read errors that have been detected on
 
       errors
        An approximate count of read errors that have been detected on


@@ -270,7 +330,7 @@ Each directory contains:
         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
         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
+       'raid_disks' number for the array indicating which position

        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.
 


@@ -293,7 +353,7 @@ in the array.  These are named
 
     rdNN
 
 
     rdNN
 

-where 'NN' is the possition in the array, starting from 0.
+where 'NN' is the position 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,
 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,


@@ -343,6 +403,15 @@ also have
       than sectors, this my be larger than the number of actual errors
       by a factor of the number of sectors in a page.
 
       than sectors, this my be larger than the number of actual errors
       by a factor of the number of sectors in a page.
 

+   bitmap_set_bits
+      If the array has a write-intent bitmap, then writing to this
+      attribute can set bits in the bitmap, indicating that a resync
+      would need to check the corresponding blocks. Either individual
+      numbers or start-end pairs can be written.  Multiple numbers
+      can be separated by a space.
+      Note that the numbers are 'bit' numbers, not 'block' numbers.
+      They should be scaled by the bitmap_chunksize.
+

 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
 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