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

[Wendy Cheng]

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 ...

-- Wendy