[CentOS] disk I/O problems with LSI Logic RAID controller

Ross Walker rswwalker at gmail.com
Thu Feb 11 15:30:43 UTC 2010

On Feb 11, 2010, at 2:46 AM, Andrzej Szymanski <szymans at agh.edu.pl>  

> 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.


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