[CentOS] nfs slow?

Bill Campbell centos at celestial.com
Thu Dec 11 02:05:51 UTC 2008


On Wed, Dec 10, 2008, nate wrote:
>John Kordash wrote:
>>> 2.) Use TCP, UDP Transmits are often slow these days. (mount
>>> option tcp)
>>
>> Hmm, care to share any references for this?  I'd be reaching for NFS over
>> TCP in a long-haul type environment, but would run it over UDP otherwise.
>
>At least in my case, both of the vendors I am using for high
>performance NFS (BlueArc, and Exanet) have tcp as a best
>practice. Exanet actually runs on top of CentOS 4.4 though
>does not use the linux NFS stack.

We started using tcp with nfs about five years ago, largely to
cure a problem where a system running SuSE 9.0 Pro with multiple
IP addresses on the NIC was responding to NFS UDP packets from
one of the aliased IP addresses, not the primary.  This caused
NFS mounts by OS X clients to fail as they expected to get the
UDP packets back from the same IP to which they sent.  Using tcp
naturally fixed this, and I never got around to figuring out why
the replies were coming from the aliases IP address.

We use NFS mounted home Maildir directories on a system with
about 10,000 e-mail accounts, and a cluster of 4 machines handling
incoming e-mail, with most of the postfix configuration files NFS
mounted as well.  These handle about 100,000 incoming messages a
day without problems (a fair number of which are dropped without
delivery after checking with spamassassin).  There are about
182,000 IMAP/POP3 daily logins to check mail.  Load averages are
fairly low on all the systems, and the incoming mail queues
rarely get over five messages with most of the delivery time
being spamassassin checking using a central bayesian database.

The central server that has all the home directories generally
runs with a load average around 0.50 (a 4-year old SLES 9.2
system with a single Intel(R) Pentium(R) 4 CPU 3.00GHz, 2GB RAM
with 7,200 RPM Seagate Barracuda SATA drives, hardly a high
performance machine compared to what we're building today.

Bill
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