Networker

Re: [Networker] Oscillating Thruput

2002-09-11 22:59:25
Subject: Re: [Networker] Oscillating Thruput
From: "Jeffrey S. Jewett" <spider AT UMD5.UMD DOT EDU>
To: NETWORKER AT LISTMAIL.TEMPLE DOT EDU
Date: Wed, 11 Sep 2002 17:47:33 -0400
Thanks for the response.

The most striking feature of this phenomenon is the regularity of the
oscillations.  Graphically (as with perfmeter)   we see spikes of high
transfer (and cpu and packets and whatever) at definite intervals
separated by long valleys of low transfer.

One of the more interesting events unfolded like this.   3 clients
writing to a tape (DLT8000 drive) at about 4.5 MB/sec for several hours,
when the tape became full.   At that time (essentially) all traffic stopped
while NetWorker validated the last block written,  unloaded the full tape,
and loaded a new tape.   So,  for several minutes,  no traffic.

When writing started on the new tape,  we saw the oscillating thruput.
250 KB/sec for about 10 minutes,  then 1-2 minutes of 5MB/sec,  then repeat.

During this transition,  nothing else changed.  No new clients.   No changes
to configuration,  nothing.   Definitely weird.

It hasn't happened for the last week,  probably because I was all geared up
to investigate.

The fact that the transition occurred after a pause of several minutes
(to switch tapes) has to be significant.    Does anyone know if nsrmmd
does anything to "load-level" the various data streams that are
being multiplexed?

- jeff

---------------------------------------------------------------------------
Jeffrey S. Jewett                               Phone:  301.405.3054
UNIX Support Group,  DCS/OIT                    Fax  :  301.314.9220
Rm 1311, Computer and Space Sciences Bldg       Email:  spider AT umd DOT edu
University of Maryland
College Park, MD  20742-2411

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