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Strange disk performance issue

December 13th, 2011 - 04:40 am ET by Frank | Report spam
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Hi list,
hoping for help, I'm experiencing a strange performance issue on debian
squeeze. The host is running 2.6.32-5-amd64 on a Xen enterprise cluster,
filesystem lies on a NetApp storage mounted using ISCSI. Other virtual
hosts on that cluster does not have the same performance problems.

As soon as I start to copy i.e. a 2GB file local or to a remote host,
the iowait is rising and the host feels jerking.

sar reports %iowait > 60

Activating block_dump for a minute (echo 1 > /proc/sys/vm/block_dump)
shows me that the process causing the iowait is jbd2 which is part of
the ext4 filesystem.

Any ideas howto tweak the fs for better performance?

Regards
Frank


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#1 Stan Hoeppner
December 13th, 2011 - 02:30 pm ET | Report spam
On 12/13/2011 3:24 AM, Frank wrote:

Hi list,
hoping for help, I'm experiencing a strange performance issue on debian
squeeze. The host is running 2.6.32-5-amd64 on a Xen enterprise cluster,
filesystem lies on a NetApp storage mounted using ISCSI. Other virtual
hosts on that cluster does not have the same performance problems.

As soon as I start to copy i.e. a 2GB file local or to a remote host,
the iowait is rising and the host feels jerking.

sar reports %iowait > 60

Activating block_dump for a minute (echo 1 > /proc/sys/vm/block_dump)
shows me that the process causing the iowait is jbd2 which is part of
the ext4 filesystem.

Any ideas howto tweak the fs for better performance?



Ext4 isn't the source of the problem but simply the messenger in this
case. Try the deadline and noop elevators and see if that helps. The
default CFQ elevator is known to suck. Also, post the block layer
device driver you're using to access the virtual disk.

Stan


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