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md: create externally visible flags for supporting hot-replace.

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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>
This commit is contained in:
NeilBrown 2011-12-23 10:17:51 +11:00
parent b8321b68d1
commit 2d78f8c451
4 changed files with 125 additions and 39 deletions
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7
include/linux/raid/md_p.h
View file

@ -277,7 +277,10 @@ struct mdp_superblock_1 {
*/
#define MD_FEATURE_RESHAPE_ACTIVE 4
#define MD_FEATURE_BAD_BLOCKS 8 /* badblock list is not empty */
#define MD_FEATURE_ALL (1|2|4|8)
#define MD_FEATURE_REPLACEMENT 16 /* This device is replacing an
* active device with same 'role'.
* 'recovery_offset' is also set.
*/
#define MD_FEATURE_ALL (1|2|4|8|16)
#endif