Tuning ext3 for a FC SAN?

[Kenny Lussier]

Hi All,

I am not a filesystem/performance expert by any means, so I am hoping
that I can pick up some tips and pointers here. We are currently
evaluating a SAN, and the performance is less then stellar. We have
simulated our production environment, which is:

RHEL 4 (x86_64) u7 running the 2.6.9-67.ELsmp kernel
Dual quad-core Xeon 3.16GHz CPUs
16GB of RAM.
15K SAS internal drives RAID1
Two single port FC QLogic HBA's (4G/s model)
Two Brocade FC SAN switches
SAN from <un-named vendor>  with 96 400GB 10K drives

The problem that we are seeing is that the descrepancy in I/O
performance between local disk and the SAN throughput seems way too
high. Using IOZone, we are getting 80MB/sec throughput for rewrites of
16-32MB files, with a 4K block size on the local disks. When running
the exact same tests against the SAN, we are seeing 14MB/sec
throughput. I expect to see a difference between local and remote
storage, but that seems to be outside the realm of normalcy.

So, my question is, is there something that I need to do to tune the
ext3 filesystem? Are there options that I should use when I create the
file system to optimize it, or mount options that should be in fstab
to increase performance? Are there any pointers anyone may have for
optimizing a system for use as a database server connected to a FC
SAN?

TIA,
Kenny