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From: brown@noao.arizona.edu (Mike Brown)
Newsgroups: comp.dcom.lans,comp.unix.wizards
Subject: NFS performance: a question
Keywords: NFS, performance, read/write asymmetry
Message-ID: <663@noao.UUCP>
Date: 31 Jan 88 22:40:08 GMT
Organization: National Optical Astronomy Observatories, Tucson, AZ
Lines: 51


Why is the transfer rate when a process writes to a remote NFS file 3-4 times
smaller than the transfer rate when reading a remote NFS file?

	- Is this asymmetry a characteristic of NFS?
	- Do Ultrix(2.0) and 4.3BSD/NFS from Mt. Xinu both have brain damaged
		NFS implementations?
	- Is my test brain damages?


I am surprized at the difference in the tranfer rate for writing a file
compared to reading a file.  I understand that creating/writing a file in
Unix is slower because of extra overhead involved during file allocation.
The difference I see is far greater than the difference in performance for
reads/writes on a local file system in Unix.  The disks I use have effective
transfer rates of about 280-300 Kilobytes/sec.

The test I ran was:

    writing:
	time /bin/cp /local/2_megabytes /remote/2_megabytes
	time /bin/cp /local/2_megabytes /remote/2_megabytes
	time /bin/cp /local/2_megabytes /remote/2_megabytes

    reading:
	time /bin/cp /remote/2_megabytes /local/2_megabytes
	time /bin/cp /remote/2_megabytes /local/2_megabytes
	time /bin/cp /remote/2_megabytes /local/2_megabytes

The test was run between microvaxes running 4.3BSD from Mt. Xinu
and it was also run between microvaxes running Ultrix 2.0.  The systems
were running multiuser with no other user processes active.

The transfer rates were:	reading (110-90 Kbytes/sec)
				writing (20-25 Kbytes/sec)


	Regards,
	Mike Brown		Biomedical Computer Lab.
				Washington University
				700 S. Euclid Ave.
				St. Louis, MO  63110
				(314) 362-2135


uucp:		uunet!wucs1!brown	or	{...}!noao!brown
internet:	brown@noao.arizona.edu


( Please excuse my posting this from arizona. )
( News out of Wash. Univ. is broken. )