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From: mjr@hussar.dco.dec.com (Marcus J. Ranum)
Newsgroups: comp.unix.internals
Subject: Re: NFS and slow links
Message-ID: <1991Feb26.143813.3980@decuac.dec.com>
Date: 26 Feb 91 14:38:13 GMT
References: <1991Feb26.033503.12885@Citicorp.COM>
Organization: Digital Equipment Corp., Washington Ultrix Resource Center
Lines: 21

dsamperi@Citicorp.COM (Dominick Samperi) writes:

>[...] Further investigation
>revealed that what made all of the difference was whether or
>not the user's home directory was local or NFS-mounted. More
>precisely, the performance hit resulted from the need to write
>the output executable file (about 10Megs) to an NFS-mounted
>directory.

	This is because NFS writes are done synchronously - IE: the
calling process waits until the write has been performed on the server
before it returns. You can somewhat offset the damage by running the
block I/O demon on the client (biod(8)) but as long as you have to
do NFS writes you'll see some performance loss. Another approach some
take is to add battery-backed RAM caches to machines, to speed up
synchronous writes on the servers, thereby speeding up the clients
as well. Legato's PrestoCache (available for a variety of machines,
available as a built-in on some DEC servers) can speed NFS performance
up to 300% in some cases.

mjr.


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