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OSR5 better nfs performance reducing nbuf buffer cache

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From: Bela Lubkin <belal@sco.com>
Subject: Re: Comments on RAID configuration wanted
Date: Fri, 10 Jan 2003 21:45:34 GMT
References: <34545947.0301090803.256187c1@posting.google.com>
<rt9r1vs2mv92o67pe37e7oauv3ibr4bsg0@4ax.com> Jeff Liebermann wrote: > Methinks you are optimizing > the wrong area. SCO ships with the disk buffers (NBUF) set at what I > would consider to be overly conservative. That was fine when RAM was > cheap, but makes no sense in these days of commodity ECC RAM. May I > suggest you read up on past comments regarding tweaking NBUF and NHBUF > in comp.unix.sco.misc. > <http://groups.google.com/groups?as_q=NBUF&as_ugroup=comp.unix.sco.misc> > Methinks you will find a rather spectacular improvement in disk > performance with an increase in these. On small boxes, my > rule-o-thumb is about 30-50% of RAM goes to disk buffering. There's > apparently a 450MByte maximum (NBUF=450000). Also, make sure you have > a really good UPS as leaving live data in the disk buffers is not a > great idea.

The other night I quadrupled the performance of a machine by _reducing_
NBUF from 400000 to 7000.  Until this is fixed, be aware that the NFS
client code on OSR5 gives you a huge performance _penalty_ for large
buffer caches.  As long as your machine isn't doing a lot of NFS client
I/O (accessing files "over there" via NFS), it shouldn't be a problem.

Technobabble: every time the NFS client code opens a remote inode, it
tells the OSR5 buffer cache to purge old references to that inode.  The
particular routine it calls walks linearly through every buffer in the
cache.  With 400000 buffers, that takes a bit of time.  This particular
application was reading zillions of small files over NFS, compounding
the problem greatly.

NFS client machines which don't actually do a lot of NFS file accessing
should be fine.  Accessing large files via NFS should be fine.  Systems
whose whole lives are devoted to reading small files over NFS may
benefit from sharply _reduced_ NBUF.  Hopefully this will be fixed in a
future NFS update (won't be fixed in 507 out the gate).


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