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SubjectRe: very poor ext3 write performance on big filesystems?
Andreas Dilger wrote:
> I'm CCing the linux-raid mailing list, since I suspect they will be
> interested in this result.
>
> I would suspect that the "journal guided RAID recovery" mechanism
> developed by U.Wisconsin may significantly benefit this workload
> because the filesystem journal is already recording all of these
> block numbers and the MD bitmap mechanism is pure overhead.
>

Thanks for sharing these numbers. I think use of a bitmap is one of
those things which people have to configure to match their use,
certainly using a larger bitmap seems to reduce the delays, using an
external bitmap certainly help, especially on an SSD. But on a large
array, without a bitmap, performance can be compromised for hours during
recovery, so the administrator must decide if normal case performance is
more important than worst case performance.

--
Bill Davidsen <davidsen@tmr.com>
"Woe unto the statesman who makes war without a reason that will still
be valid when the war is over..." Otto von Bismark




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