[Veritas-bu] Tape Drive speed

2003-07-06 13:03:40
Subject: [Veritas-bu] Tape Drive speed
From: joe AT spamcop DOT net (Johnny Oestergaard)
Date: Sun, 06 Jul 2003 19:03:40 +0200
Not that I have ever used SDLT drives, but I agree that getting max drive 
performance out of any system is difficult (except in a lab where you have 
control of every single bit)

Most tapedrives today are fast. In our installation we use STK 9940B and 
they write data at 30MB/s (before compression) and they easyly do 70MB/s in 
a lab (but not in real world windows installations)

Our installation is pure Windows and all our havy servers are sitting on 
1Gbps on a BlackDiamond 6808, but we hardly see more then 15 MB/s. Our 
biggest performance problem today is that windows is much too slow in 
open/close operation of files. Backup of 2.000.000 files each less then 
16Kbyte takes forever.

By the way start/stop is very fast on the STK 9940B drives and we hardly 
see any tape errors at all. Shoe-shining is not a big problem for us. When 
we used DLT tape problems was a daily thing.

We use FC connections to our drives, but I would expect that you have to be 
carefull about how many drives you connect to each SCSI cntl. Pushing a lot 
of data over a SCSI cntl. is not always the fastest thing in the world.

You should look into blksize, buffers, multiplexing and your network.


At 18:28 02-07-2003 -0400, veritas-bu AT jasons DOT us wrote:
>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
>---There is no TRUTH.  There is no REALITY.  There is no CONSISTENCY.---
>    ---There are no ABSOLUTE STATEMENTS   I'm very probably wrong.---
>Veritas-bu maillist  -  Veritas-bu AT mailman.eng.auburn DOT edu

<Prev in Thread] Current Thread [Next in Thread>