[rescue] VS80 DLT tape drive question

Curtis H. Wilbar Jr. rescue at hawkmountain.net
Fri Dec 14 08:54:35 CST 2007

Mr Ian Primus wrote:
> --- "Curtis H. Wilbar Jr." <rescue at hawkmountain.net>
> wrote:
>> It is not streaming well.... so not sure what I'd
>> need to tweak (just using
>> tar now under Linux).  I also only have it connected
>> up to an Adaptec
>> 2940U ... I would have though this drive does
>> ultra... but dmesg seems to
>> indicate it running at 10.0 MB/s.  Although I'd
>> think that should be fine
>> as it only backs up 3-6MB/sec (3 non compressed, 6
>> compressed at 2:1).
>> It is the only device on the controller... so I
>> think it should be fine...
>> Anyone have any success in tweaking parameters via
>> mt/tar/etc to get them
>> to stream well ?
> A couple things - have you checked in the BIOS
> settings for the Adaptec controller, and made sure
> that it's set for higher speed mode on that SCSI ID?
> Are you connecting it to the machine through a 50 pin
> or 68 pin cable?

(smacks forehead)... I didn't check that... I'll have to do that.

I'm using a 50 pin to 68 pin cable to mate up to the Dell external
drive, and I'm using a active (but not LVD) 68 pin terminator.

(I chose this method as I had my Sun DLT4000 drive on it which
is 68 pin externally but 50 pin internally... so I figured why 'waste'
a 2940UW :-) )

hrm... I should also check the BIOS to see if term for the card is
on/off/auto... I didn't check that either... or parity even... guess I
was in a hurry or something, as I can't believe I neglected to
check those settings (after all, it is a used SCSI card, no telling
what the settings would be).
> Since that drives should have a pretty good buffer,
> this may not apply, but it helped me vastly when
> dealing with an old SCSI TK50 under Linux:
> mt -f /dev/nst0 drvbuffer 1
> Turning on the host buffer made the TK50 write the
> same data in about 1/20th the time. Before, it just
> kept shoeshining.

I might have to experiment... even with Ultra SCSI, 6M/sec should
be attainable.... so if the drive tops out (in compressed mode) at 6M/sec
I shouldn't be shoeshining even at 10M/sec SCSI.

I did have the tar running as time tar ... so I got:
313m34.661s to backup 43678188K (as reported by du -sk)

That translates to: 42654.48M/18814.66s = 2.27M/sec

Most of the data was .tgz, .iso, .zip, etc... so I'd expect to see not
much over 3MB/sec... so... maybe not bad considering there were
periods of shoeshining.

Now... on bulk erasing DLTs... any idea of a Radio Shack bulk eraser
is going to have the 'punch' required ?  works great on floppies (I've
'rescued' lots of floppies that would format with bad sectors by bulk
erasing and reformatting)... but I seem to recall trying a VCR tape at
one point and it not being very effective.

on bulk erasing.... bulk erase top, top and bottom, or the sides ?  Which
way will orient the magnetic field of the bulk erase for maximum
effect ?

-- Curt

> -Ian
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