[5019] in linux-scsi channel archive
Re: Q: DLT7000 tapedrives under Linux
daemon@ATHENA.MIT.EDU (Richard Fish)
Wed Oct 28 12:06:52 1998
Date: Wed, 28 Oct 1998 08:22:02 -0700
From: Richard Fish <rjf@estinc.com>
To: Linux SCSI <linux-scsi@vger.rutgers.edu>
Jon Lewis wrote:
>
> On Tue, 27 Oct 1998, Pieter Krul wrote:
>
> > The DLT7000 drives as I know them are able to write data in
> > so called 'streaming mode' at about 5MB/s uncompressed.
> >
> > The only way I've had the 7000 to work is in the 'normal' tape-
> > drive mode, so the drive starts to write, stops, waits a while,
> > writes, stops etcetera, so not what it should have done.
> >
> > The performance of these drives in this way can be called quite
> > poorly (1.5MB/s).
I never thought I'd see the day when 1.5Mb/sec tape throughput would be
called "poor"! ;)
> With the really fast tape drives, the problem is usually that you can't
> give them the data fast enough for them to keep streaming. There is a
Absolutely! one other thing you should do is time test a backup to
/dev/null. A couple of examples:
# bru -cf /dev/null /
# tail /var/log/bruexeclog
or with tar:
# time tar -cf - / | dd of=/dev/null bs=1k
Your throughput should be at least twice as fast as the rated speed of
the tape drive, i.e, at least 10Mb/sec -- more if you want to use the
hardware compression on the drive. Otherwise, buffering may help a
little, but you'll never get anywhere near the rated speed of the
drive...
--
Richard Fish Enhanced Software Technologies, Inc.
Software Developer 4014 E Broadway Rd Suite 405
rjf@estinc.com Phoenix, AZ 85040
(602) 470-1115 http://www.estinc.com
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