Re: XFS: Abysmal write performance because of excessive seeking (allocation groups to blame?)

Martin Steigerwald
2012-04-07T18:57:41Z

Am Freitag, 6. April 2012 schrieb Stefan Ring:
> > thanks for the detailed report.
>
> Thanks for the detailed and kind answer.
>
> > Can you try a few mount options for me both all together and if you
> > have some time also individually.
> >
> > -o inode64
> >
> > This allows inodes to be close to data even for >1TB
> > filesystems. It's something we hope to make the default soon.
>
> The filesystem is not that large. It’s only 400GB. I turned it on
> anyway. No difference.
>
> > -o filestreams
> >
> > This keeps data written in a single directory group together.
> > Not sure your directories are large enough to really benefit
> > from it, but it's worth a try.
> > -o allocsize=4k
> >
> > This disables the agressive file preallocation we do in XFS,
> > which sounds like it's not useful for your workload.
>
> inode64+filestreams: no difference
> inode64+allocsize: no difference
> inode64+filestreams+allocsize: no difference :(
>
> > For metadata intensive workloads like yours you would be much better
> > using a non-striping raid, e.g. concatentation and mirroring instead
> > of raid 5 or raid 6. I know this has a cost in terms of "wasted"
> > space, but for IOPs bound workload the difference is dramatic.
>
> Hmm, I’m sure you’re right, but I’m out of luck here. If I had 24
> drives, I could think about a different organization. But with only 6
> bays, I cannot give up all that space.
>
> Although *in theory*, it *should* be possible to run fast for
> write-only workloads. The stripe size is 64 KB (4x16), and it’s not
> like data is written all over the place. So it should very well be
> possible to write the data out in some reasonably sized and aligned
> chunks. The filesystem partition itself is nicely aligned.

And is XFS aligned to the RAID 6?

What does xfs_info display on it?

--
Martin 'Helios' Steigerwald - http://www.Lichtvoll.de
GPG: 03B0 0D6C 0040 0710 4AFA B82F 991B EAAC A599 84C7