[Linux-cluster] GFS performance.

[Vikash Khatuwala]

Hello,

OS : CentOS 5.2
FS : GFS
Journals : 4
Nodes : 1 (currently testing)
iSCSI Target : Dell MD3000i
Disks : 5 x SAS 15K RPM 300GB.

I would like to know what is the expected performance penalty for using GFS.

Currently I have a single node cluster for testing using the lock_dlm 
over an iSCSI RAID 5 disk system. Ive create 2 volumes on the same 
RAID 5 disk set 1st one is GFS and the second one is ext3. Ive used 
"fio" for my performance testing and found that ext3 is about 4 times 
faster then GFS. The test is using random reads of 4KB. If instead I 
use sequential reads of 256K then the performance is very close to 
the ext3 filesystem, but thats far from our practical environment.

This seems to be quite extreme and so would like to know how to tune 
the performance on GFS. Ive tried guidelines from:
http://www.redhat.com/promo/summit/2008/downloads/pdf/Thursday/Summit08presentation_GFSBestPractices_Final.pdf

However they only improve CPU utilization but disk IO performance 
does not improve by much.

Now I need to make a decision to go with GFS or not, clearly at 4 
times less performance we cannot afford it, also it doesn't sound 
right so would like to find out whats wrong.

Thanks and hope to get some pointers.

Regards,
Vikash.