linux-toradex.git/Documentation/md.txt, branch v2.6.27.27

md: Tidy up rdev_size_store a bit:

2008-07-21T04:22:18+00:00

 - used strict_strtoull in place of simple_strtoull
 - use my_mddev in place of rdev->mddev (they have the same value)
and more significantly,
 - don't adjust mddev->size to fit, rather reject changes which make
   rdev->size smaller than mddev->size

Adjusting mddev->size is a hangover from bind_rdev_to_array which
does a similar thing.  But it really is a better design to insist that
mddev->size is set as required, then the rdev->sizes are set to allow
for that.  The previous way invites confusion.

Signed-off-by: NeilBrown

Make sure all changes to md/dev-XX/state are notified

2008-06-27T22:31:44+00:00

The important state change happens during an interrupt
in md_error.  So just set a flag there and call sysfs_notify
later in process context.

Signed-off-by: Neil Brown

Make sure all changes to md/degraded are notified.

2008-06-27T22:31:43+00:00

When a device fails, when a spare is activated, when
an array is reshaped, or when an array is started,
the extent to which the array is degraded can change.

Signed-off-by: Neil Brown

Make sure all changes to md/sync_action are notified.

2008-06-27T22:31:41+00:00

When the 'resync' thread starts or stops, when we explicitly
set sync_action, or when we determine that there is definitely nothing
to do, we notify sync_action.

To stop "sync_action" from occasionally showing the wrong value,
we introduce a new flags - MD_RECOVERY_RECOVER - to say that a
recovery is probably needed or happening, and we make sure
that we set MD_RECOVERY_RUNNING before clearing MD_RECOVERY_NEEDED.

Signed-off-by: Neil Brown

Make sure all changes to md/array_state are notified.

2008-06-27T22:31:36+00:00

Changes in md/array_state could be of interest to a monitoring
program.  So make sure all changes trigger a notification.

Exceptions:
   changing active_idle to active is not reported because it
      is frequent and not interesting.
   changing active to active_idle is only reported on arrays
      with externally managed metadata, as it is not interesting
      otherwise.

Signed-off-by: Neil Brown

md: introduce get_priority_stripe() to improve raid456 write performance

2008-04-28T15:58:42+00:00

Improve write performance by preventing the delayed_list from dumping all its
stripes onto the handle_list in one shot.  Delayed stripes are now further
delayed by being held on the 'hold_list'.  The 'hold_list' is bypassed when:

  * a STRIPE_IO_STARTED stripe is found at the head of 'handle_list'
  * 'handle_list' is empty and i/o is being done to satisfy full stripe-width
    write requests
  * 'bypass_count' is less than 'bypass_threshold'.  By default the threshold
    is 1, i.e. every other stripe handled is a preread stripe provided the
    top two conditions are false.

Benchmark data:
System: 2x Xeon 5150, 4x SATA, mem=1GB
Baseline: 2.6.24-rc7
Configuration: mdadm --create /dev/md0 /dev/sd[b-e] -n 4 -l 5 --assume-clean
Test1: dd if=/dev/zero of=/dev/md0 bs=1024k count=2048
  * patched:  +33% (stripe_cache_size = 256), +25% (stripe_cache_size = 512)

Test2: tiobench --size 2048 --numruns 5 --block 4096 --block 131072 (XFS)
  * patched: +13%
  * patched + preread_bypass_threshold = 0: +37%

Changes since v1:
* reduce bypass_threshold from (chunk_size / sectors_per_chunk) to (1) and
  make it configurable.  This defaults to fairness and modest performance
  gains out of the box.
Changes since v2:
* [neilb@suse.de]: kill STRIPE_PRIO_HI and preread_needed as they are not
  necessary, the important change was clearing STRIPE_DELAYED in
  add_stripe_bio and this has been moved out to make_request for the hang
  fix.
* [neilb@suse.de]: simplify get_priority_stripe
* [dan.j.williams@intel.com]: reset the bypass_count when ->hold_list is
  sampled empty (+11%)
* [dan.j.williams@intel.com]: decrement the bypass_count at the detection
  of stripes being naturally promoted off of hold_list +2%.  Note, resetting
  bypass_count instead of decrementing on these events yields +4% but that is
  probably too aggressive.
Changes since v3:
* cosmetic fixups

Tested-by: James W. Laferriere 
Signed-off-by: Dan Williams 
Signed-off-by: Neil Brown 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

md: allow a maximum extent to be set for resyncing

2008-02-06T18:41:18+00:00

This allows userspace to control resync/reshape progress and synchronise it
with other activities, such as shared access in a SAN, or backing up critical
sections during a tricky reshape.

Writing a number of sectors (which must be a multiple of the chunk size if
such is meaningful) causes a resync to pause when it gets to that point.

Signed-off-by: Neil Brown 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

md: allow reshape_position for md arrays to be set via sysfs

2007-05-09T19:30:57+00:00

"reshape_position" records how much progress has been made on a "reshape"
(adding drives, changing layout or chunksize).

When it is set, the number of drives, layout and chunksize can have
two possible values, an old an a new.

So allow these different values to be visible, and allow both old and new to
be set: Set the old ones first, then the reshape_position, then the new
values.

Signed-off-by: Neil Brown 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

Fix typos in Documentation/: 'Q'-'R'

2006-10-03T20:54:15+00:00

This patch fixes typos in various Documentation txts. The patch addresses
some words starting with the letters 'Q'-'R'.

Signed-off-by: Matt LaPlante 
Acked-by: Randy Dunlap 
Signed-off-by: Adrian Bunk

Fix typos in Documentation/: 'N'-'P'

2006-10-03T20:52:05+00:00

This patch fixes typos in various Documentation txts. The patch addresses
some words starting with the letters 'N'-'P'.

Signed-off-by: Matt LaPlante 
Acked-by: Randy Dunlap 
Signed-off-by: Adrian Bunk