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Hi List,
We've just deployed a new syslog server infrastructure consisting of
two hosts -- one NFS server that has a large disk array attached via
fibre channel and one NFS client that receives syslog messages,
mounts the server's disk, and writes to the NFS exported filesystem.
Statistics grinding is done on the server so as to avoid impacting
collection of syslog messages. The NFS server and client are
connected to each other via a private back-to-back GigE.
The problem is that NFS is causing a 10x to 15x packet amplification
on the link that carries the NFS traffic. By this I mean that for
each syslog message received by the collector, there are somewhere
between 10 and 15 (sometimes less, sometimes more) packets on the
private NFS link. About half of these are full-MTU packets.
When the client receives a syslog message, the sequence of
operations on the NFS link appears to be:
client -> server: write
server -> client: ok
client -> server: commit
server -> client: ok
client -> server: access
server -> client: ok
client -> server: read
server -> client: ok + 4k-16k worth of data
Looking at the packet contents, it appears to be fetching back the
last few blocks of the log file.
My guess is that this is the client keeping its NFS cache fresh.
The client is never, ever, ever going to read that file (or any file
on that filesystem) other than the bare minimum required to open it
for writing and rotate the log files.
Is there a way to disable client-side caching? I've looked, and
can't seem to find one. Or, do I have this wrong and there is
something else that is causing this?
Any insight would be very much appreciated....
Thanks!
--eli
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