On 20/07/2014 21:36, Roman Mamedov wrote:
On Sun, 20 Jul 2014 21:15:31 +0200
Bob Marley <bobmarley@xxxxxxxxxxxxx> wrote:
Hi TM, are you doing other significant filesystem activity during this
rebuild, especially random accesses?
This can reduce performances a lot on HDDs.
E.g. if you were doing strenous multithreaded random writes in the
meanwhile, I could expect even less than 5MB/sec overall...
I believe the problem here might be that a Btrfs rebuild *is* a strenuous
random read (+ random-ish write) just by itself.
Mdadm-based RAID would rebuild the array reading/writing disks in a completely
linear manner, and it would finish an order of magnitude faster.
Now this explains a lot!
So they would just need to be sorted?
Sorting the files of a disk from lowest to highers block number prior to
starting reconstruction seems feasible. Maybe not all of them together
because they will be millions, but sorting them in chunks of 1000 files
would still produce a very significant speedup!
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