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Re: xfs: very slow after mount, very slow at umount

To: xfs@xxxxxxxxxxx
Subject: Re: xfs: very slow after mount, very slow at umount
From: Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>
Date: Wed, 26 Jan 2011 23:17:13 -0600
In-reply-to: <4D40EB2F.2050809@xxxxxxxxxxxx>
References: <4D40C8D1.8090202@xxxxxxxxxxxx> <20110127033011.GH21311@dastard> <4D40EB2F.2050809@xxxxxxxxxxxx>
User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.9.2.13) Gecko/20101207 Thunderbird/3.1.7
Mark Lord put forth on 1/26/2011 9:49 PM:

> agcount=7453

That's probably a bit high Mark, and very possibly the cause of your problems.
:)  Unless the disk array backing this filesystem has something like 400-800
striped disk drives.  You said it's a single 2TB drive right?

The default agcount for a single drive filesystem is 4 allocation groups.  For
mdraid (of any number of disks/configuration) it's 16 allocation groups.

Why/how did you end up with 7452 allocation groups?  That can definitely cause
some performance issues due to massively excessive head seeking, and possibly
all manner of weirdness.

-- 
Stan

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