From: Dave Chinner <david@fromorbit.com>
To: Richard Scobie <richard@sauce.co.nz>
Cc: xfs@oss.sgi.com
Subject: Re: XFS over LVM over md RAID
Date: Fri, 10 Sep 2010 11:30:26 +1000 [thread overview]
Message-ID: <20100910013026.GA24409@dastard> (raw)
In-Reply-To: <4C89668E.6010800@sauce.co.nz>
On Fri, Sep 10, 2010 at 10:58:22AM +1200, Richard Scobie wrote:
> Using the latest, stable versions of LVM2 and xfsprogs and the
> 2.6.35.4 kernel, I am setting up lvm on a 16 drive, 256k chunk md
> RAID6, which has been used to date with XFS directly on the RAID.
>
> mkfs.xfs directly on the RAID gives:
>
> meta-data=/dev/md8 isize=256 agcount=32,
> agsize=106814656 blks
> = sectsz=4096 attr=2
> data = bsize=4096 blocks=3418068864, imaxpct=5
> = sunit=64 swidth=896 blks
> naming =version 2 bsize=4096 ascii-ci=0
>
> which gives the correct sunit and swidth values for the array.
>
> Creating an lv which uses the entire array and mkfs.xfs on that, gives:
>
> meta-data=/dev/vg_local/Storage isize=256 agcount=13,
> agsize=268435455 blks
> = sectsz=512 attr=2
> data = bsize=4096 blocks=3418067968, imaxpct=5
> = sunit=0 swidth=0 blks
> naming =version 2 bsize=4096 ascii-ci=0
Hmmm - it's treating MD very differently to the LVM volume -
different numbers of AGs, different sunit/swdith. Did you
build xfsprogs yourself? Is it linked against libblkid or libdisk?
Or it might be that LVM is not exporting the characteristic of the
underlying volume. Can you check if there are different parameter
values exported by the two devices in /sys/block/<dev>/queue?
> Limited testing using dd and bonnie++ shows no difference in write
> performance whether I use sunit=64/swidth=896 or sunit=0/swidth=0 on
> the lv.
These benchmarks won't realy show any difference on an empty
filesystem. It will have an impact on how the filesystems age and
how well aligned the IO will be to the underlying device under more
complex workloads...
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
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next prev parent reply other threads:[~2010-09-10 1:29 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-09-09 22:58 XFS over LVM over md RAID Richard Scobie
2010-09-10 0:25 ` Michael Monnerie
2010-09-10 0:52 ` Richard Scobie
2010-09-10 1:14 ` Richard Scobie
2010-09-10 1:30 ` Dave Chinner [this message]
2010-09-10 2:29 ` Richard Scobie
2010-09-10 14:24 ` Eric Sandeen
2010-09-10 21:42 ` Richard Scobie
2010-09-10 22:19 ` Stan Hoeppner
-- strict thread matches above, loose matches on Subject: below --
2010-09-10 23:08 Richard Scobie
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