Veritas-bu

[Veritas-bu] "Waited for full buffer" messages

2002-07-17 14:21:04
Subject: [Veritas-bu] "Waited for full buffer" messages
From: TMKing AT forestoil DOT com (Ty King)
Date: Wed, 17 Jul 2002 12:21:04 -0600
I've been making attempts to improve the throughput of my backups as I think
there's definitely some room do to so considering our hardware
configuration.  In the BPTM logs I'm looking at the "waited for full buffer"
entries with numbers ranging from 40,000 for small jobs to 700,000+ times
for a 400GB backup on our file server.  This seems like way too much.  I've
compared it with the "waited for empty buffer" numbers which are generally
below 100.  It seems to me there should be a better middle ground.

My setup is Veritas 3.4.1 master/media server on a Win2k server which is
also our primary file server with the 400+ GB to back up.  It's attached
through LVD SCSI to a Spectra Logic Gator 12K with three AIT-3 drives with
two on one bus and one on it's own.  My avg throughput is around 10K/s for
this direct attached server.  I had expected I'd be doing much better than
this, especially considering compression.

My backups from the other Win2k clients over 100Mb ethernet to the library
avg around 3K/s, which also seems tremendously slow.  The only exception to
this being my Exchange server which seems to get about 8K/s, but it's also
only backing up a dump of the Exchange database as one contiguous file.
That might explain it's better performance.

I've been toying with the buffer size and number.  Most people seem to
recommend using 64K buffers, but I've also tried reducing the buffer size as
that seems to be the suggestion when getting a large number of "waited for
full buffer" events.  Most references state that decreasing the size and
number of buffers would help reduce the number of events, but I've seen
little to no difference in doing so.  I'm now back to running with the
default 16 buffers at 64K.  Could there be something else hanging this up?

Just looking for someone with some real experiences with this instead of
what a tech doc tells me.


Thanks,
Ty King

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