Re: Tape Type

On Wed, Mar 15, 2006 at 01:03:10PM -0500, Carl Holzhauer wrote:
> >If you plan to use this drive with the compressor on you should not
> ALSO use software compression.  The >tapes capacity for gzipped data
> would be closer to 50GB without the compressor.  You would need
> >another amtapetype run without HW compression to check the actual
> capacity.
> 
> Is there a way that I can turn off hardware compression in Amanada? I do
> not have that option on the tape loader I use.
>  
> 
> -----Original Message-----
> From: owner-amanda-users AT amanda DOT org
> [mailto:owner-amanda-users AT amanda DOT org] On Behalf Of Jon LaBadie
> Sent: Tuesday, March 14, 2006 3:52 PM
> To: amanda-users AT amanda DOT org
> Subject: Re: Tape Type
> 
> On Tue, Mar 14, 2006 at 01:23:17PM -0500, Carl Holzhauer wrote:
> > Just wanted to post this incase some one else has the same backup 
> > device.
> >  
> > Backup device is a Comapq Storage Works SSL2020 Tapes are Compaq AIT 
> > 50GB amtapetype returns the following:
> > 
> > define tapetype unknown-tapetype {
> >     comment "just produced by tapetype prog (hardware compression on)"
> >     length 43605 mbytes
> >     filemark 0 kbytes
> >     speed 5583 kps
> > }
> 
> The typical 15% loss of native capacity when random data is fed through
> the tape drive's compressor due to its expansion of the random data
> rather than compression.
> 
> If you plan to use this drive with the compressor on you should not ALSO
> use software compression.  The tapes capacity for gzipped data would be
> closer to 50GB without the compressor.  You would need another
> amtapetype run without HW compression to check the actual capacity.
> 
> If, OTOH, you don't plan to gzip (SW compression) your amanda dumps and
> plan to let the drive's compressor do the job, then the above tapetype
> is meaningless.  Depending on the compress- ability of your data, it
> could be anywhere from 50 to 150GB.
> It will be just a guesstimate.  If amanda keeps filling your tapes,
> lower your guess.

Hardware drivers are not amanda's thing.
It only uses what is provided by the OS.
Otherwise you would be limited to what
is provided by amanda.  (which is the
case with some backup systems)

How your system does it varies with the OS.
Maybe mt command, maybe something like stinit,
maybe by specifying certain device names.

-- 
Jon H. LaBadie                  jon AT jgcomp DOT com
 JG Computing
 4455 Province Line Road        (609) 252-0159
 Princeton, NJ  08540-4322      (609) 683-7220 (fax)