Re: Slow writing speed on LTO4 SAS tape

Dear Silviu,

Writing zero's to a tape-drive with hardware-compression enabled by default
is not a good measurement-example.
Try writing real data, not zero's that can easily be compressed by the drive
to a "minimal" write-operation..

See also the st/mtinit-help-pages:
http://linux.die.net/man/8/stinit
There are a lot of configuration parameters you can adjust to get the
maximum out of your drive.

Regards
  Frank

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Von: [email protected]
[mailto:[email protected]] Im Auftrag von Silviu
Marin-Caea
Gesendet: Donnerstag, 25. Februar 2010 12:24
An: [email protected]
Betreff: Re: [suse-sles-e] Slow writing speed on LTO4 SAS tape

On Wed, 24 Feb 2010 16:08 -0300, "Ciro Iriarte" <[email protected]>
wrote:

> Hmmm, just to make sure, do a test reading from memory.
> 
> dd if=/dev/zero of=/dev/st0

time dd if=/dev/zero of=/dev/nst0 bs=1M count=4096
4096+0 records in
4096+0 records out

real    0m26.642s
user    0m0.002s
sys     0m1.245s

Would that be relevant?  The drives have hardware compression activated.
 So this command would show just how fast the drive can compress a
stream of zero and write to tape much less actual data than 4GB.

The speed computes to around 157 MB/s, the device specification is 120
MB/s

Is this rationale correct?  Am I missing something?
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