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authorNeilBrown <neilb@suse.de>2011-12-23 10:17:51 +1100
committerNeilBrown <neilb@suse.de>2011-12-23 10:17:51 +1100
commit2d78f8c451785f030ac1676a18691896b59c69d8 (patch)
tree4dfe69115b2ca2fb8be2a671e7c8399c3925fcb9 /Documentation
parentb8321b68d1445f308324517e45fb0a5c2b48e271 (diff)
downloadlinux-2d78f8c451785f030ac1676a18691896b59c69d8.tar.bz2
md: create externally visible flags for supporting hot-replace.
hot-replace is a feature being added to md which will allow a device to be replaced without removing it from the array first. With hot-replace a spare can be activated and recovery can start while the original device is still in place, thus allowing a transition from an unreliable device to a reliable device without leaving the array degraded during the transition. It can also be use when the original device is still reliable but it not wanted for some reason. This will eventually be supported in RAID4/5/6 and RAID10. This patch adds a super-block flag to distinguish the replacement device. If an old kernel sees this flag it will reject the device. It also adds two per-device flags which are viewable and settable via sysfs. "want_replacement" can be set to request that a device be replaced. "replacement" is set to show that this device is replacing another device. The "rd%d" links in /sys/block/mdXx/md only apply to the original device, not the replacement. We currently don't make links for the replacement - there doesn't seem to be a need. Signed-off-by: NeilBrown <neilb@suse.de>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/md.txt22
1 files changed, 18 insertions, 4 deletions
diff --git a/Documentation/md.txt b/Documentation/md.txt
index fc94770f44ab..993fba37b7d1 100644
--- a/Documentation/md.txt
+++ b/Documentation/md.txt
@@ -357,14 +357,14 @@ Each directory contains:
written to, that device.
state
- A file recording the current state of the device in the array
+ 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 or it has unacknowledged bad
- blocks
+ a detected fault, or it has unacknowledged bad
+ blocks
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.
+ requests if there are no other options.
This applies only to raid1 arrays.
blocked - device has failed, and the failure hasn't been
acknowledged yet by the metadata handler.
@@ -374,6 +374,13 @@ Each directory contains:
This includes spares that are in the process
of being recovered to
write_error - device has ever seen a write error.
+ want_replacement - device is (mostly) working but probably
+ should be replaced, either due to errors or
+ due to user request.
+ replacement - device is a replacement for another active
+ device with same raid_disk.
+
+
This list may grow in future.
This can be written to.
Writing "faulty" simulates a failure on the device.
@@ -386,6 +393,13 @@ Each directory contains:
Writing "in_sync" sets the in_sync flag.
Writing "write_error" sets writeerrorseen flag.
Writing "-write_error" clears writeerrorseen flag.
+ Writing "want_replacement" is allowed at any time except to a
+ replacement device or a spare. It sets the flag.
+ Writing "-want_replacement" is allowed at any time. It clears
+ the flag.
+ Writing "replacement" or "-replacement" is only allowed before
+ starting the array. It sets or clears the flag.
+
This file responds to select/poll. Any change to 'faulty'
or 'blocked' causes an event.