NFS performance

[Dave Hitz]

In article <7887 at lynx.UUCP> m5 at lynx.uucp (Mike McNally) writes:
> A brief question for those experienced with NFS environments: do you expect
> the operation of copying a file with "cat" from a remotely mounted file
> system to /dev/null to be (A) about the same as using rcp, (B) about the
> same as for a file from a local disk, or (C) something else (?).  I'm not
> really interested in special situations, just this straightforward (and
> admittedly overly simple) test.

In general:

    For small files, the cat should win because there is a fair amount
    of overhead involved in starting up the rcp connection.  For very
    large files, the two should be similar, although rcp might have
    a small edge because TCP has better buffering and window size
    adjustment algorithms than NFS.

In specific, there are some cases where the above isn't true:

    (1) In SunOS 4.0 (and higher), cat doesn't actually do reads in
        the case where the output goes to /dev/null.  So on a SunOS
        client, the cat will be instant while the rcp will be slow.
	Using 'dd bs=8k' instead of 'cat' forces the I/O to occur.

					cat	dd	rcp
		4 meg file        	0:00	0:07	0:10
		16K file		0:00	0:00	0:02

    (2) With Auspex NS 5000 servers, NFS requests go through dedicated NFS
	hardware, whereas rcp requests go to a general purpose UNIX
	processor.  As a result the dd  will be much faster than the rcp.

					cat	dd	rcp
		4 meg file 		0:00	0:07	0:38
		16K file		0:00	0:00	0:05

	Both rcp results are slower than the ones above because the
	Auspex UNIX processor is a 68K, whereas the ones above come
	from a SPARC server.

There are probably more exceptions for other combinations of
hardware/software, but these are the two that come to mind
immediately.

I would say, if you have NFS use it.

Dave Hitz					home: 408-739-7116
UUCP: {uunet,mips,sun,bridge2}!auspex!hitz 	work: 408-492-0900
-- 
Dave Hitz					home: 408-739-7116
UUCP: {uunet,mips,sun,bridge2}!auspex!hitz 	work: 408-492-0900