Re: [Bug 14830] When other IO is running sync times go to 10 to 20 minutes

[Chris Lee <cslee-list@cybericom.co.uk>]

bugzilla-daemon@bugzilla.kernel.org wrote:
> http://bugzilla.kernel.org/show_bug.cgi?id=14830
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> --- Comment #3 from Michael Godfrey <godfrey@isl.stanford.edu>  2010-01-18 23:58:09 ---
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>> This problem prevents production use of systems using this kernel.
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>> evokes a question: Do you have a kernel which behaved better for you? Which
>> one?
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> Yes.  RHEL5.4 does not show this problem.  It is the production
> system that works in this environment.
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> The response above is disappointing.  Is sync response of 20 minutes,
> including several task timeouts to be considered "normal?"
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>> If you think the time is inappropriately long, we can have a look at it
>> but for that we'd need much more details like amount and nature of data writen
>> (many small files vs a few large ones), time it takes sync to complete, speed
>> of disks for sequential IO...
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> I am sorry to have to tell you that in this environment we do not
> deal in exclusively small or large files, we actually have quite a
> few of both. When an rsync which transfers about 50GB of files of
> various sizes is running, the hung condition is continuous until the rsync
> completes.  This is just a pretty typical load.  You could try it
> yourself.  No special sizes of files are required.  I think I
> mentioned that the ext4 LVM is a RAID 50 3ware 9650SE-8LPML,
> with 8 2T drives.  Its throughput for reading and writing is good
> when the system is not locked up.
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>   
Is it possible that it is something allong the lines of what is 
described at this link:
http://notemagnet.blogspot.com/2008/08/linux-write-cache-mystery.html

If so a runtime adjustment might help you out.

Chris.