On Fri, Jun 02, 2006 at 07:08:39AM -0700, Joe Donner (sent by Nabble.com) 
enlightened us:
> Dear all,
> 
> I've just run amtapetype -f /dev/nst0 for Amanda to generate a tapetype
> definition for an HP Storageworks SDLT 320 tape drive.
> 
> The results came back as:
> 
> define tapetype unknown-tapetype {
> comment "just produced by tapetype prog (hardware compression on)"
> length 135040 mbytes
> filemark 39 kbytes
> speed 2272 kps
> }
> 
> amtapetype did slightly complain about hardware compression being enabled,
> but I couldn't see a way of disabling that.
> 
> Would you, in your experience, think that this tapetype definition seems
> accurate and "acceptable" to use for real backups? This is the last
> outstanding piece of the Amanda puzzle before putting Amanda into operation.
> 
> The tape drive's capacity is 160Gb uncompressed and 320Gb compressed,
> according to its specifications. So I'm not too sure about the length 135040
> mbytes mentioned in the generated tapetype. Won't this cause Amanda to not
> use the drive's full capacity?
> 
> Any advice will be much appreciated.
> 

Yes, disable hardware compression. The reason amanda only detected about
135GB of your 160GB tape is because compressing already-compressed data
usually causes it to expand. The only exception I've seen is LTO, which is
smart enough to leave it alone. Disabling hardware compression happens at
the OS or tape drive level. You can use mt to turn it of on most Unix-like
systems, or better yet disable it with a dip switch/jumper on the drive
itself.

2nd suggestion: forget the number 320GB. It is purely marketing. Your tapes
will hold 160GB of data. The data may be compressed, and you may be able to
fit 320GB on there, you may be able to fit 400GB on there, or you may only
be able to fit 162GB on there. It all depends on your data and how
compressable it is. 

Matt

-- 
Matt Hyclak
Department of Mathematics 
Department of Social Work
Ohio University
(740) 593-1263