>>>>> On Thu, 22 May 2008 13:35:52 -0400, Alex Chekholko said:
> 
> 
> I just ran some dd tests, and it seems like block size makes a big
> difference, and with 64KB block size I get ~25MB/s.  An LTO-4 tape is loaded
> into /dev/nst1 which is an LTO-4 IBM ULT3580-TD4 drive:
> 
> # date; dd if=/dev/zero of=/dev/nst1 bs=1024k count=10240; date
> Thu May 22 12:56:38 EDT 2008
> 10240+0 records in
> 10240+0 records out
> 10737418240 bytes (11 GB) copied, 137.136 seconds, 78.3 MB/s
> Thu May 22 12:58:55 EDT 2008
> # date; dd if=/dev/zero of=/dev/nst1 bs=64k count=10240; date
> Thu May 22 13:02:38 EDT 2008
> 10240+0 records in
> 10240+0 records out
> 671088640 bytes (671 MB) copied, 26.8409 seconds, 25.0 MB/s
> Thu May 22 13:03:05 EDT 2008
> # date; dd if=/dev/zero of=/dev/nst1 bs=2048k count=10240; date
> Thu May 22 13:09:47 EDT 2008
> 10240+0 records in
> 10240+0 records out
> 21474836480 bytes (21 GB) copied, 245.657 seconds, 87.4 MB/s

Bweare that testing from /dev/zero might not give a realistic result if the
drive has compression switched on, because the phyical tape will hardly move.
It will test the interface card's speed nicely :-)

It is probably better to make a large file containing real data, e.g. tar from
/usr/lib.  You could also compress the file with gzip, which will prevent the
drive from doing any compression.

__Martin

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