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authorNeilBrown <neilb@suse.de>2009-03-31 14:33:13 +1100
committerNeilBrown <neilb@suse.de>2009-03-31 14:33:13 +1100
commit97e4f42d62badb0f9fbc27c013e89bc1336a03bc (patch)
tree04cc809702a6b080c417c4ddf605642bbf7de521 /REPORTING-BUGS
parent43b2e5d86d8bdd77386226db0bc961529492c043 (diff)
md: occasionally checkpoint drive recovery to reduce duplicate effort after a crash
Version 1.x metadata has the ability to record the status of a partially completed drive recovery. However we only update that record on a clean shutdown. It would be nice to update it on unclean shutdowns too, particularly when using a bitmap that removes much to the 'sync' effort after an unclean shutdown. One complication with checkpointing recovery is that we only know where we are up to in terms of IO requests started, not which ones have completed. And we need to know what has completed to record how much is recovered. So occasionally pause the recovery until all submitted requests are completed, then update the record of where we are up to. When we have a bitmap, we already do that pause occasionally to keep the bitmap up-to-date. So enhance that code to record the recovery offset and schedule a superblock update. And when there is no bitmap, just pause 16 times during the resync to do a checkpoint. '16' is a fairly arbitrary number. But we don't really have any good way to judge how often is acceptable, and it seems like a reasonable number for now. Signed-off-by: NeilBrown <neilb@suse.de>
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