Re: [PATCH] xfs: improve sync behaviour in face of aggressive dirtying

Michael Monnerie
2011-06-21T07:21:53Z

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On Dienstag, 21. Juni 2011 Dave Chinner wrote:
> > The minor one is that we always flush all work items and not just
> > those on the filesystem to be flushed. This might become an issue
> > for lager systems, or when we apply a similar scheme to fsync,
> > which has the same underlying issue.
>
> For sync, I don't think it matters if we flush a few extra IO
> completions on a busy system.

Couldn't that be bad on a system with mixed fast/slow storage (say 15k
SAS and 7.2k SATA), where on the busy fast SAS lots of syncs occur and
lead to extra I/O on the SATA disks? Especially if there are 16 SAS
disks in an array with RAID-0 against 4 SATA disks in RAID-6, to say the
worst. If the SATAs are already heavy used (say >=50%), those extra
writes could bring them to their knees.

I'm not sure how often syncs occur though, maybe that's why Dave says it
shouldn't matter? AFAIK, databases generate heavy syncs though.

--
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Michael Monnerie, Ing. BSc

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