Journal-guided RAID resync
Posted Nov 26, 2009 21:00 UTC (Thu) by neilbrown
In reply to: Journal-guided RAID resync
Parent article: Journal-guided RAID resync
Surely this is not the case in the (fairly common) case of out-of-order writes? This sounds like exactly the sort of situation that caused the ext4 kerfuffle earlier this year.
I don't see how out-of-order writes complicate the question ... maybe I'm missing something. A key question that must be understood is "what data is valid", and in the case of multiple parallel writes pending when a crash happens, there are lots of combinations that are all equally valid.
On a different note, can anyone explain to me why running a check or (god forbid) rebuild on a RAID array takes like a dozen times longer than reading/writing the contents of all the disks?
This is not my experience. If you post specifics to firstname.lastname@example.org
you will probably get a useful reply.
The only explanation for what you describe that immediately occurs to me is that fact that the check/repair code deliberately slows down when any other IO is active so as not to inconvenience that IO, but you probably know that already.
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