sync() in 2.6.38.5

[Joe Landman]

On 11/29/2011 02:17 PM, Paul Anderson wrote:
> Hi all,
>
> 2.6.38.5 (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).

Try

	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
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Scalable Informatics Inc.
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