On Sat, Sep 17, 2005 at 11:25:48PM -0400, Florian Lengyel wrote:
> Here's the post-mortem: I've been using a hand-me-dowm
> Spectra Logic 2K. No matter what tape I tried in drive 0
> (the only one of two that my AMANDA configuration seems
> to recognize) I had I/O errors. Even an innocuous command such as
> 
> mt -f /dev/nst0 compression off
> 
> [by the way, the argument "off" is worth a small fortune in
> consulting fees, since it has to be guessed]
> 
> Resulted in an I/O error. Such things are often caused by
> hardware trouble. After checking cables, interface card seating,
> and other things, I tried using the cleaning tape. 
> 
> Problem solved.

You wouldn't think a 'compression off' request would have
any involvement with possibly dirty heads.  Here is a guess,
I've seen some tape drives that when an error happens flag
the error and refuse to do anything until it is cleared.
At one client they had a DLT drive.  Anything went wrong
and the "clean drive" light came on.  Then you could do
nothing unless you cleaned it or 'I think' there was some
manual way to turn off the light.  Maybe power off/on :)

BTW you mention you have other ?drives? not being seen?
Based on replies here, most linux kernels default to only
scanning LUN 0 on the scsi buss.  Some configuation change
lets it scan others.  Similarly on my Solaris system, by
default only scsi IDs 0-7 are scanned for tape drives.
Again a config setting allows IDs 8-15 to be scanned.

Maybe something similar is your problem.

-- 
Jon H. LaBadie                  jon AT jgcomp DOT com
 JG Computing
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