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Re: suddenly slow writes on XFS Filesystem

To: Stefan Priebe <s.priebe@xxxxxxxxxxxx>
Subject: Re: suddenly slow writes on XFS Filesystem
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Mon, 7 May 2012 11:34:56 +1000
Cc: "xfs@xxxxxxxxxxx" <xfs@xxxxxxxxxxx>
In-reply-to: <4FA63DDA.9070707@xxxxxxxxxxxx>
References: <4FA63DDA.9070707@xxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Sun, May 06, 2012 at 11:01:14AM +0200, Stefan Priebe wrote:
> Hi,
> since a few days i've experienced a really slow fs on one of our
> backup systems.
> I'm not sure whether this is XFS related or related to the
> Controller / Disks.
> It is a raid 10 of 20 SATA Disks and i can only write to them with
> about 700kb/s while doing random i/o.

What sort of random IO? size, read, write, direct or buffered, data
or metadata, etc? iostat -x -d -m 5 and vmstat 5 traces would be
useful to see if it is your array that is slow.....

> I tried vanilla Kernel 3.0.30
> and 3.3.4 - no difference. Writing to another partition on another
> xfs array works fine.
> Details:
> #~ df -h
> /dev/sdb1             4,6T  4,4T  207G  96% /mnt

Your filesystem is near full - the allocation algorithms definitely
slow down as you approach ENOSPC, and IO efficiency goes to hell
because of a lack of contiguous free space to allocate from.

> #~ df -i
> /dev/sdb1            4875737052 4659318044 216419008  96% /mnt

You have 4.6 *billion* inodes in your filesystem?

> Any ideas?

None until I understand your workload....


Dave Chinner

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