Usually I prefer to test using a large precompressed (zip/tar.gz) file and
not to disable compression. This is closer to the reality eliminating
possible (with low chance) problems due to different settings. It also
helps to reveal the expand after compression issues.

Pipe the output of tar+gzip to a large enough file and perform the
`dd`-test again. I was able to fully load up to two FC-attached LTO-1
drives from a single system with or without compression. Maybe to utilize
successfully several LTO-2 drives would be a real challenge :-()

Zlatko Krastev
IT Consultant






Richard Sims <rbs AT BU DOT EDU>
Sent by: "ADSM: Dist Stor Manager" <ADSM-L AT VM.MARIST DOT EDU>
22.07.2003 22:19
Please respond to "ADSM: Dist Stor Manager"


        To:     ADSM-L AT VM.MARIST DOT EDU
        cc:
        Subject:        Re: Tape performance


>>I am wondering if there is something in TSM that throttles the tape
>>performance we should be getting.  I can do a dd test from the operating
>>system to the tape drive and with that receive 2 GB per minute (32
MB/sec)
>>but when I do a test through TSM, I only get 1 GB per minute.

>The test to move data from the operating system was just a 10GB file,
>although it was all zero's.
...

Thanks, that extra info helps a lot...
The T9840B FICON Tape Drive Specifications that I see on the vendor web
site
quote "Performance, native 19 MB/sec".  I thought the 32 MB/s was a high
number.  I suspect that you did not disable tape drive compression in your
all-zero's test, and so ended up with a number which was a great test of
your
FC, but not the drive->media.  In context, your ~16 MB/s TSM speed seems
excellent, then.  I'd be happy with that number.

Customers who also have 9840B drives might want to chime in on their
experiences.

  Richard Sims, BU