[Beowulf] OT: LTO Ultrium (3) throughput?

Joe Landman landman at scalableinformatics.com
Wed Jun 18 20:24:20 EDT 2008


David Mathog wrote:
> If any of you have an LTO Ultrium-3 drive what kind of speeds are you
> observing?  On one Linux system here (kernel 2.6.24-19) we have an
> HP Ultrium-3 attached to an Adaptec ASC-29320ALP U320 controller.
> There is nothing else on that SCSI bus, termination and cable seem good.
> Getting into scsi-select from the BIOS shows everything set to 320.
> No error messages or warnings are appearing. Yet:
> 
>   dd if=/dev/zero of=/dev/nst0 bs=8192 count=10000
> 
> only moves 21.3MB/sec.  The HP documentation indicates 432GB/hour,
> (compressed) which is 120 Mb/sec, so we're off by 6X (or maybe 3X for
> 2:1 compression, either way, a lot).  The system's CPU and memory
> aren't rate limiting as
> 
>   dd if=/dev/zero of=/dev/null bs=8192 count=10000
> 
> moves 6.9GB/sec.  
> 
> Any thoughts where the bottleneck might be? 

Have you adjusted the block size up?  maybe try

dd if=/dev/zero of=/dev/nst0 bs=8M count=1000

this is about 8 GB, so it hopefully shouldn't take too long.  At 21 
MB/s, this is about 50 seconds per gigabyte, so if this takes 400 
seconds, you may have a problem.

This said, the tape drive numbers we see quoted are "best case" 
scenarios, with optimal block sizes, a strong wind at the tapes back, 
and no monopole flux nearby.  Burning incense may or may not help the 
speed, YMMV...

This said, have you tried the "obvious" tests, such as what does lsscsi 
report, and lscpi -v for that adapter, and ...

-- 
Joseph Landman, Ph.D
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Scalable Informatics LLC,
email: landman at scalableinformatics.com
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