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Date:      Wed, 28 Nov 2001 09:10:17 -0600
From:      Bob Willcox <bob@immure.com>
To:        Courtney Thomas <ccthomas@flash.net>
Cc:        Ted Mittelstaedt <tedm@toybox.placo.com>, Anthony Atkielski <anthony@freebie.atkielski.com>, freebsd-questions@FreeBSD.ORG
Subject:   Re: SCSI tape back that works under FreeBSD
Message-ID:  <20011128091017.A89511@luke.immure.com>
In-Reply-To: <3C03961A.2060109@flash.net>; from ccthomas@flash.net on Tue, Nov 27, 2001 at 08:33:14AM -0500
References:  <000101c17714$2abf0ea0$1401a8c0@tedm.placo.com> <3C03961A.2060109@flash.net>

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I've used Exabyte 8mm drives for years on FreeBSD (as well as some other
OSes) and haven't had streaming problems with them so long as I make
certain that they are either set to a large blocksize or better yet, to
variable blocksize. If you have the drive set to a small fixed blocksize
it won't stream (on input or output). You can check/set this with the mt
command. For example with my drive I get:

$ mt status
Mode      Density              Blocksize      bpi      Compression
Current:  0x27:Mammoth         variable       77611    IDRC
---------available modes---------
0:        0x27:Mammoth         variable       77611    IDRC
1:        0x27:Mammoth         variable       77611    IDRC
2:        0x27:Mammoth         variable       77611    IDRC
3:        0x27:Mammoth         variable       77611    IDRC
---------------------------------
Current Driver State: at rest.
---------------------------------
File Number: 44 Record Number: 0        Residual Count 0

with mt and as you can see the blocksize is variable. Also, I never
bother with programs such as buffer or team as I find that dump does a
good job of buffering its output for the tape drive.

One further note: In my experience the newer Mammoth Exabyte drives (I
haven't tried a Mammoth2 yet) are _much_ better than all of the other
8mm and 4mm drives that I have used. These have a higher capacity (a
native capacity of 20GB for Mammoth and 60GB for Mammoth2), higher data
rates (3MB/s for Mammoth and I believe about double that for Mammoth2),
and, in my experience, have been significantly more reliable. Unlike
the older Exabyte drives (which were modified Sony VCR transports as I
understand it), these drives have no capstans or pinch rollers and move
the tape faster and with less stress/wear.

Bob

On Tue, Nov 27, 2001 at 08:33:14AM -0500, Courtney Thomas wrote:
> 
> Speaking of Exabyte drives, I [am trying to :-)]use the 8500 [no 
> compression] but..............
> can't get it to stream, after trying many permutations [and a couple of 
> days] of possible commands.
> 
> I've also erased the [new] tape, cleaned the drive with an Exabyte 
> cleaning cartridge, changed the cable, etc.
> 
> BTW, an Athlon 750mhz w/256MB ram, AHA1520 card. I realize this is a low 
> end card but it has worked in another machine OK. The drive is almost 
> unused since new and appears to work satisfactorily other than no streaming.
> 
> I've read the dump, st, and buffer man pages and the st page in 
> particular documents the driver functionality in extremis [for only a 
> user :-)]  nevertheless it is clear that there are many, many 
> potentially troublesome variables that it seems to me only a proficient 
> C programmer with lots of time and a real good working knowledge of 
> things SCSI could probe.
> 
> The command I'm using is...............
>        dump 0ub 64 /<dir> | `buffer -s 16k > /dev/tape`
> 
> Since you use a DAT at home and are familiar with [at least the Exabyte] 
> 8mm drives, hopefully you can point me to a resolution.
> 
> Also, since this is a discontinued product, Exabyte is no help, now, 
> though they were vigorously supportive when I first got the drive.
> 
> Hopefully,
> 
> Courtney Thomas
> 
> 
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-- 
Bob Willcox             Boucher's Observation:
bob@vieo.com               He who blows his own horn always plays the music
Austin, TX                 several octaves higher than originally written.

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