NFS Help! Terrible performance with sync, fast performance with async

[Ron McKeever]

Are you using tcp as transport?

 

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From: redhat-sysadmin-list-bounces at redhat.com
[mailto:redhat-sysadmin-list-bounces at redhat.com] On Behalf Of Chris Wornell
Sent: Sunday, November 19, 2006 1:59 AM
To: redhat-sysadmin-list at redhat.com
Subject: NFS Help! Terrible performance with sync,fast performance with
async

 

I've got a problem that I've spent quite a bit of time on, though I'm not an
expert at NFS. In summary, operations that require meta-data changes (such
as file/directory creations/deletions), perform extremely slow over sync,
but over 10x faster using async.

I have two systems, connected to a GigE switch using intel pro 1000 NICs
(jumbo frames is currently not enabled on any of the points). 

The NFS server is a dual-core opteron system with 1GB of RAM and 3x300 SAS
disk RAID-5 on a Perc5/i controller with 256MB battery backed cache (write
cache is enabled). The file system is ext3. I've configured nfsd to spawn 32
processes upon startup. I'm using defaults for export the nfs shares, no
changes to rsize or wsize.

The NFS client is a dual Xeon with 4GB of RAM and a single 7200rpm SATA
disk. Both systems are running RHEL WS 3 Update 8 and kernel
2.4.21-47.0.1.ELsmp. 

For testing, I'm using bonnie++. The following are some sample test results
that sum up the problem:

Test on NFS server directly (not NFS loopback)
-Sequential File Creation: 2976
-Sequential File Deletion: N/A
-Random File Creation: 3077
-Random File Deletion: 9922

NFS test with sync enabled
-Sequential File Creation: 39
-Sequential File Deletion: 79
-Random File Creation: 39
-Random File Delection: 65

NFS test with async enabled
-Sequential File Creation: 575
-Sequential File Deletion: 1718
-Random File Creation: 543
-Random File Deletion: 1228

Based on the local performance of the NFS server, it does not appear the IO
setup is the culprit. My understanding of the sync operation is a commit
happens which means the NFS server doesn't reply back until the change has
actually been committed to stable storage. There is something happening
behind the scenes though which is causing a huge delay before the NFS server
replies back the commit was complete.

This question is actually work related and I'm planning to put the NFS
server into production, but I'd rather not use async, even with a UPS and
dual PSU's on the server. With the newer nfs-utils, sync is the default
option as well so it seems like sync should perform relatively well.

Another question is I don't quite understand how the data corruption happens
if a power loss occurs on an NFS server using async. Even with sync, data
transferred over the wire maybe loss if the nfs server gets shut down before
that data is committed. Can anyone go into more detail on how the data
corruption happens?

Thanks a bunch!

 

Thanks,

Chris Wornell
Network Administrator, Information Technology
Peerless Systems Corporation
 <http://www.peerless.com/> http://www.peerless.com
office: 310.727.5723
fax: 310.727.5715
 <mailto:cwornell at peerless.com> mailto:cwornell at peerless.com 

 

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