[5293] in linux-scsi channel archive
Re: DAT trouble
daemon@ATHENA.MIT.EDU (Pete Popov)
Sat Dec 5 04:02:07 1998
Date: Fri, 04 Dec 1998 10:19:52 -0800
From: Pete Popov <ppopov@redcreek.com>
To: Jon Lewis <jlewis@inorganic5.fdt.net>
CC: Richard Fish <rjf@estinc.com>, Michael Lausch <mla@gams.co.at>,
linux-scsi@vger.rutgers.edu
Jon,
Jon Lewis wrote:
> On Thu, 3 Dec 1998, Richard Fish wrote:
>
> > Another test is to run a backup, turning off software and hardware
> > compression with "mt -f /dev/st0 datcompression off". Your throughput
> > to the drive should be ~366K/sec with DDS-II.
Not all DDS2 drives are this slow :-)
> With DDS1 you will get
> > ~175K/sec.
>
> It doesn't seem to be that simple. Sony claims the 7000 can do 1.5MB/s.
> In real life, I got 40MB/min, which is about twice the speed I used to get
> from older Archive based DATs.
The lower than expected performance is most likely due a small SCSI transfer
size. I increased the default 32K to 128K, recompiled the st driver, and use 128K
with tar and regularly get 70MB/s with my SDT-7000.
The 1.5MB/s (90MB/min) spec is the actual transfer rate to tape. You'll need an
extremely fast host with low SCSI command overhead to get close to that.
Pete
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