On Feb 11, 2010, at 2:46 AM, Andrzej Szymanski szymans@agh.edu.pl wrote:
On 2010-02-09 18:15, Fernando Gleiser wrote:
Every time we try to copy some large file to the storage-based file system, the disk utilization see-saws up to 100% to several seconds of inactivity, to climb up again to 100% and so forth. Here are a snip from the iostat -kx 1:
Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq- sz avgqu-sz await svctm %util sdb1 0.00 133811.00 0.00 1889.00 0.00 513660.00 543.84 126.24 65.00 0.47 89.40
The iostat output looks good to me for the RAID setup you have. I'd look for the problem in a different place:
note the output of cat /proc/sys/vm/dirty_background_ratio and try echo 1 > /proc/sys/vm/dirty_background_ratio whether it helps.
Excellent suggestion, on machines with lots of memory the default dirty background ratio is way too big, and needs to be tuned down for both data integrity in the event of a system failure and performance of the underlying storage configuration.
Take into account the RAID setup, write-back cache size and time it takes to empty it to disk and pick a dirty background ratio somewhere in between.
-Ross