Merge branch 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab...

[safe/jmp/linux-2.6] / Documentation / md.txt

diff --git a/Documentation/md.txt b/Documentation/md.txt
index 9ae9e40..1da9d1b 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


@@ -175,9 +175,24 @@ 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
 
      of 2.  This can only be set while assembling an array
 

+  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.
+
+  reshape_position
+     This is either "none" or a sector number within the devices of
+     the array where "reshape" is up to.  If this is set, the three
+     attributes mentioned above (raid_disks, chunk_size, layout) can
+     potentially have 2 values, an old and a new value.  If these
+     values differ, reading the attribute returns
+        new (old)
+     and writing will effect the 'new' value, leaving the 'old'
+     unchanged.
+

   component_size
      For arrays with data redundancy (i.e. not raid0, linear, faulty,
      multipath), all components must be the same size - or at least
   component_size
      For arrays with data redundancy (i.e. not raid0, linear, faulty,
      multipath), all components must be the same size - or at least


@@ -193,11 +208,6 @@ 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.
 

-  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
   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


@@ -214,8 +224,8 @@ All md devices contain:
    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
    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 arrive, the array is marked as 'dirty' before the write
-     commenses.  This is known as 'safe_mode'.
+     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.
      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.


@@ -226,6 +236,11 @@ All md devices contain:
      writing the word for the desired state, however some states
      cannot be explicitly set, and some transitions are not allowed.
 
      writing the word for the desired state, however some states
      cannot be explicitly set, and some transitions are not allowed.
 

+     Select/poll works on this file.  All changes except between
+       active_idle and active (which can be frequent and are not
+       very interesting) are notified.  active->active_idle is
+       reported if the metadata is externally managed.
+

      clear
          No devices, no size, no level
          Writing is equivalent to STOP_ARRAY ioctl
      clear
          No devices, no size, no level
          Writing is equivalent to STOP_ARRAY ioctl


@@ -259,29 +274,6 @@ All md devices contain:
          like active, but no writes have been seen for a while (safe_mode_delay).
 
 
          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}
-     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,
-     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
-     a locally set or system-wide value.
-
-   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
-     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.
-
-

 As component devices are added to an md array, they appear in the 'md'
 directory as new directories named
       dev-XXX
 As component devices are added to an md array, they appear in the 'md'
 directory as new directories named
       dev-XXX


@@ -305,15 +297,25 @@ Each directory contains:
              writemostly - device will only be subject to read
                         requests if there are no other options.
                         This applies only to raid1 arrays.
              writemostly - device will only be subject to read
                         requests if there are no other options.
                         This applies only to raid1 arrays.

+             blocked  - device has failed, metadata is "external",
+                        and the failure hasn't been acknowledged yet.
+                        Writes that would write to this device if
+                        it were not faulty are blocked.

              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.
        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.

+       Writing "blocked" sets the "blocked" flag.
+       Writing "-blocked" clear the "blocked" flag and allows writes
+               to complete.
+
+       This file responds to select/poll. Any change to 'faulty'
+       or 'blocked' causes an event.

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


@@ -330,7 +332,7 @@ 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.
 


@@ -345,7 +347,7 @@ Each directory contains:
         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.
+        written, it will be rejected.

 
 
 An active md device will also contain and entry for each active device
 
 
 An active md device will also contain and entry for each active device


@@ -353,7 +355,7 @@ 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,


@@ -394,6 +396,19 @@ also have
        'check' and 'repair' will start the appropriate process
            providing the current state is 'idle'.
 
        'check' and 'repair' will start the appropriate process
            providing the current state is 'idle'.
 

+      This file responds to select/poll.  Any important change in the value
+      triggers a poll event.  Sometimes the value will briefly be
+      "recover" if a recovery seems to be needed, but cannot be
+      achieved. In that case, the transition to "recover" isn't
+      notified, but the transition away is.
+
+   degraded
+      This contains a count of the number of devices by which the
+      arrays is degraded.  So an optimal array with show '0'.  A
+      single failed/missing drive will show '1', etc.
+      This file responds to select/poll, any increase or decrease
+      in the count of missing devices will trigger an event.
+

    mismatch_count
       When performing 'check' and 'repair', and possibly when
       performing 'resync', md will count the number of errors that are
    mismatch_count
       When performing 'check' and 'repair', and possibly when
       performing 'resync', md will count the number of errors that are


@@ -412,6 +427,45 @@ also have
       Note that the numbers are 'bit' numbers, not 'block' numbers.
       They should be scaled by the bitmap_chunksize.
 
       Note that the numbers are 'bit' numbers, not 'block' numbers.
       They should be scaled by the bitmap_chunksize.
 

+   sync_speed_min
+   sync_speed_max
+     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,
+     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
+     a locally set or system-wide value.
+
+   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
+     value, a fraction of the process that is complete.
+     A 'select' on this attribute will return when resync completes,
+     when it reaches the current sync_max (below) and possibly at
+     other times.
+
+   sync_max
+     This is a number of sectors at which point a resync/recovery
+     process will pause.  When a resync is active, the value can
+     only ever be increased, never decreased.  The value of 'max'
+     effectively disables the limit.
+
+
+   sync_speed
+     This shows the current actual speed, in K/sec, of the current
+     sync_action.  It is averaged over the last 30 seconds.
+
+   suspend_lo
+   suspend_hi
+     The two values, given as numbers of sectors, indicate a range
+     within the array where IO will be blocked.  This is currently
+     only supported for raid4/5/6.
+
+

 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


@@ -424,3 +478,9 @@ These currently include
       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
       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

+  preread_bypass_threshold (currently raid5 only)
+      number of times a stripe requiring preread will be bypassed by
+      a stripe that does not require preread.  For fairness defaults
+      to 1.  Setting this to 0 disables bypass accounting and
+      requires preread stripes to wait until all full-width stripe-
+      writes are complete.  Valid values are 0 to stripe_cache_size.