[Linux-cluster] GFS RG size (and tuning)

Wendy Cheng wcheng at redhat.com
Fri Nov 2 20:46:54 UTC 2007


Wendy Cheng wrote:
> Jos Vos wrote:
>> On Fri, Nov 02, 2007 at 04:12:39PM -0400, Wendy Cheng wrote:
>>
>>> Also I read your previous mailing list post with "df" issue - didn't 
>>> have time to comment. Note that both RHEL 4.6 and RHEL 5.1 will have 
>>> a "fast_statfs" tunable that is specifically added to speed up the 
>>> "df" command. Give it a try. If it works well, we'll switch it from 
>>> a tunable to default (so people don't have to suffer from GFS1's df 
>>> command so much).
>>
>> OK, thanks, we'll try with 5.1.
>>
>> In the meantime we rebuilded all fs's with larger RGs (-r 2048), which
>> already improved the "df" behavior seriously.
> Sign .. everything has a trade-off. Forgot to explain this .. larger 
> RG will introduce more disk reads if RG locks (that guards disk 
> allocation) happen to get moved around between different nodes. You 
> may also have to carry more buffer head in the memory cache . If you 
> do lots of rsync, it could contribute to the lock/memory congestion.
>> Also, fs performance is not that bad w.r.t. bandwidth (our 
>> measurements were first incorrect due to 32-bit counter troubles), 
>> but operations like
>> rsync (which we do a lot) that scan large directory trees are horrable.
>> For that we'll wait for 5.1.
>>
> Thanks for the patient - let us know how it goes ...

s/patient/patience/





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