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Re: sync() in

To: xfs@xxxxxxxxxxx
Subject: Re: sync() in
From: Joe Landman <landman@xxxxxxxxxxxxxxxxxxxxxxx>
Date: Tue, 29 Nov 2011 14:33:40 -0500
In-reply-to: <CAOO4vO6sSFBxXXK1z018=ekEZpcpnZ5NT_xe3d503NjN3aHF5A@xxxxxxxxxxxxxx>
Organization: Scalable Informatics
References: <CAOO4vO6sSFBxXXK1z018=ekEZpcpnZ5NT_xe3d503NjN3aHF5A@xxxxxxxxxxxxxx>
Reply-to: landman@xxxxxxxxxxxxxxxxxxxxxxx
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:8.0) Gecko/20111110 Thunderbird/8.0
On 11/29/2011 02:17 PM, Paul Anderson wrote:
Hi all, (x64 intel, in todays case a 40TiByte SAN volume) appears to
have a bug whereby not all active metadata will be flushed even on a
quiescent machine (one that has nonetheless in the past been under
very high load).

We have tried several variations of clean shutdowns, combined with for
example the "echo 3>/proc/sys/vm/drop_caches" trick to no avail - we
still get lost files (well, 0 length files).

We have several big servers scheduled to go down shortly, and I was
wondering if there are other ideas besides just coping all recent data
to another server.

Set your vm dirty time to small values. 1 second (100 centiseconds) or so, among other things. You can also force the mount to be synchronous (kills performance though).


        mount -o remount,sync /mountpoint
        # not sure if this works with xfs though ...

        sysctl -w vm.dirty_writeback_centisecs=100
        sysctl -w vm.dirty_expire_centisecs=100
        sysctl -w vm.dirty_ratio=1

Joseph Landman, Ph.D
Founder and CEO
Scalable Informatics Inc.
email: landman@xxxxxxxxxxxxxxxxxxxxxxx
web  : http://scalableinformatics.com
phone: +1 734 786 8423 x121
fax  : +1 866 888 3112
cell : +1 734 612 4615

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