The question involved NFS over a gigabit ethernet connection and
actually had two parts:
1) How can I get the best speed from the gigabit connection for NFS,
given that it works well for FTP already?
2) How can I get NFS writes to be as fast as reads?
There were lots of responses - thanks to Pat O'Brien, William Bochnik,
Selden Ball, Steve Daniel, Serguei Patchkovskii, Andrew Boswell, and
"sysadmin_at_astro.su.se".
1) Parameters to tweak for gigabit:
Number of nfs and nfsiod threads (set in nfssetup or sysman nfs) - I had
done this already. Increasing number of nfsiod threads was helpful, up
to a point. Too many threads degrades performance, but using 15-31
instead of the default 7 was good.
NFS rsize and wsize parameters (set as an option in the mount command) -
unfortunately, these are not allowed to go higher than 8K on my system.
inet parameters tcp_recvspace and tcp_sendspace (if using TCP) or
udp_recvspace and udp_sendspace (if using UDP) (set with sysconfig or
dxkerneltuner). Didn't help me a whole lot, but may be important in some
circumstances.
alt parameter send_ticks (set with sysconfig or dxkerneltuner) - try
setting to 10 instead of the default 2500.
Interface speed (set with ifconfig) - set to 9000 instead of default
1500. This didn't work for me because the switch in the system can't
handle jumbo packets, but should be good if you have the proper
hardware.
Autonegotiate on or off for the gigabit card (set with ifconfig). Didn't
make any difference in my case, but might sometimes.
2) NFS read vs. write. The short answer is: it's not possible to get
write to go as fast as read, because:
When writing, NFS insists that each block of data be written to disk
before it will send the next block. This is safe, but slow. It would
seem to help to use bigger blocks, but since wsize is limited to 8K
(possibly 32K on some systems), one can't do much in this respect.
When reading, the read is considered complete when the data get into
memory on the receiving computer, and memory access is of course faster
than disk access. Moreover, if you are accessing the same data
repeatedly caching will come into effect and subsequent transfers will
be very fast.
The only solution to speeding up writing relative to reading would seem
to be Selden Ball's suggestion to install Prestoserve hardware and
software, which caches data to be written to disk in memory first.
Should certainly help, although it's not exactly a quick, free fix.
Information on Prestoserve is available on the Compaq web site,
http://tru64unix.compaq.com/faqs/publications/base_doc/DOCUMENTATION/V51_HTML/ARH98ATE/TITLE.HTM.
Personally, I think I will try to arrange things here to avoid use of
NFS, particularly for writing.
Marian Szebenyi
MacCHESS, Cornell University
dms35_at_cornell.edu
Received on Fri May 25 2001 - 20:47:46 NZST