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.
/johnny
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
>
>-----
>Jason K. Schechner - check out www.cauce.org 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.---
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