Creating a Load Balanced E-mail Server with NFS mounts with CentOS - how to optimize for performance?

[Patrick - South Valley Internet <patrickm@garlic.com>]

Hi all,

I'm finishing up our new load balanced e-mail server which consists of 
two Dell dual cpu Opterons NFS mounting our 1.6TB RAID 5 server - all 3 
machines run CentOS.  I have VMWare server installed on both Dell 
Opterons which both machines run a CentOS LDAP server (uses 256mb RAM), 
and a CentOS Postfix server.  I have noticed no performance loss running 
VMWare, as far as I can tell.  The reason I mention this is because I've 
had experience in the past with other applications, such as 
Trixbox/Asterisk that require you to NOT run this on a VM due to issues 
with real time processing and such.  Just want to make sure that this 
isn't the case for this scenerio (which I don't think, since I'm only 
experiencing issues on the NFS mounted directories)

Anyhow, I can successfully mount the NFS from both Postfix VM's without 
a problem.  I created a /vol/vol0/home directory on the NFS, and mount 
that to /home on both Postfix VM's.  Doing a 'ls -l' in /home takes 
forever, sometimes longer than I wish (30+ seconds, sometimes longer).  
I read the NFS performance documentation on testing the read and write 
speeds and timing them, and I've come up with these:

#####################
[root@somebox mnt]# time dd if=/dev/zero of=/home/testfile bs=16k 
count=16384
16384+0 records in
16384+0 records out

real    0m43.282s
user    0m0.010s
sys     0m2.043s



[root@somebox mnt]# time dd if=/home/testfile of=/dev/null bs=16k
16384+0 records in
16384+0 records out

real    0m22.943s
user    0m0.016s
sys     0m0.629s
####################


I've tried to set different rsize and wsize (4096, 8192, 16384, and 
32768), and it doesn't seem to be doing any different.  I've checked the 
switch settings to make sure there weren't any inconsistencies and are 
set to 100xFD.



My /etc/fstab looks like this:

xxx.yyy.com:/vol/vol0/home          /home       nfs     
rw,hard,intr,rsize=32768,wsize=32768        0 0
xxx.yyy.com:/vol/vol0/spool-mail          /spool-mail       nfs     
rw,hard,intr,rsize=32768,wsize=32768        0 0
xxx.yyy.com:/vol/vol0/spool-xxx-mqueue          /spool-mqueue       
nfs     rw,hard,intr,rsize=32768,wsize=32768        0 0


I'm concerned because there will be a lot of activity on these servers, 
and I need this to be as fast as possible.

Do I have my mountpoints defined properly?

If I need to provide hardware descriptions of my machines, let me know 
and I will do a lspci.

Thanks to everyone in advance.

Patrick



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