[Veritas-bu] Tape Drive speed

2003-07-02 18:28:50
Subject: [Veritas-bu] Tape Drive speed
From: veritas-bu AT jasons DOT us (veritas-bu AT jasons DOT us)
Date: Wed, 2 Jul 2003 18:28:50 -0400 (EDT)
On Tue, 1 Jul 2003, Mike M. wrote:

> Hi
> My system is a AIX machine running Veritas DC 4.5 and the robot use SDLT
> Drive. The connection between the server and the drive is
> scsi-controller.
> When I backup some files from Veritas Server he obtain a data transfers
> from 8 Mbytes/sec. But the SDLT Drive should accept until 11 Mbytes/sec!

SDLT drives are rated at 11mB/sec without compression and, in theory will
do 22mB/sec if you have *very* compressable data.  That said, you will
very rarely see those speeds with SDLT.  Largely it'll depend on your
data, your host's memory and CPU utilization, network speed and traffic,
etc.  Most of my SDLT installations tend to top out around 10mB/sec,
largely due to network congestion.  Gigabit is getting cheaper and is one
of the first things I recommend to clients, even if only for the media
servers and big data servers.

> As anyone a Idea about this problem? How can I resolv it and what's
> check, command or something else?

Take a look at the tuning guide available from Veritas' knowledge base to
assist you in tuning your buffering parameters.  SDLT, and other linear
drives (DLT, LTO, STK 3590, etc) don't slow down gracefully.  Either they
run at *very* fast speeds or something significantly slower due to what's
called shoe-shining.  The tape speed, as it moves by the head, isn't
variable so if the drive's buffer gets empty it has to stop the tape and
rewind to the last point where it wrote anything.  This is bad for the
tape, bad for the head and bad for performance.  Adjusting Veritas'
buffers can help ensure that the drive's hardware buffers never (or
rarely) get empty.

Hope this helps.


Jason K. Schechner  -   check out and help ban spam-mail.
"All HELL would break loose if time got hacked." - Bill Kearney 02-04-03
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