Veritas-bu

[Veritas-bu] Re: Implications of turning off s/w compresion?

2002-04-04 09:40:39
Subject: [Veritas-bu] Re: Implications of turning off s/w compresion?
From: kk_downings AT yahoo DOT com (kk downing)
Date: Thu, 4 Apr 2002 06:40:39 -0800 (PST)
So basicaly a DLT tape is a DLT tape it's not like
DDS2/DDS3 incompatibilites as far as off the shelf
goes. In other words the Density specification(7000 or
8000) is chosen when the tapes is mounted and has data
writen to it in a specific drive(7000 or 8000). This
is where the calibration track comes in I guess? Is
this corect? Also does DLT1 equate to the 7000 and
DLT2 equate to the 8000? Thanks
KK null

--- Larry Kingery <larry.kingery AT veritas DOT com> wrote:
> DLT tapes contain a calibration track.  This is used
> to store info
> about the format of the tape (e.g. 7000 vs 8000,
> compressed vs not).
> The first time you write from the beginning of the
> tape (BOT), the
> calibration track is written, and that's the format
> that will be used
> forever (sort of).  
> 
> I'm not familiar with your library, but my point is
> that it's going to
> read what's on the tape regardless of how you have
> it set.
> 
> Most DLT drives have lights that you can view to
> see, among other
> things, if compression is on.  BTW, when no tape is
> mounted, the
> compression light is off.  Perhaps your library does
> the same.
> 
> If you want to reformat a DLT, you need a drive that
> has the density
> override button.  Insert a tape, use the override
> button to force the
> density (including compression) you want, and write
> anything to the
> tape (still at BOT).  Of course, you've just lost
> anything on the
> tape.  
> 
> You'll also need to set up your OS to use
> compression (or at least
> attempt to, depends on the drive setting).  On unix,
> this is done by
> choosing the right device file.
> 
> L
> 
> P.S.  The reformatting stuff may not be necessary to
> just add/remove
> compression.  Perhaps any write from BOT will do it.
>  I really don't
> remember.  The method above will work though.
> 
> Lee Anne Pedersen writes:
> > After following this thread, I'm curious to
> experiment with h/w instead of 
> > s/w compression. I have a Compaq TL891DLX library
> with two DLT8000 drives. 
> > I've tried to turn on compression for each drive
> via the system menu, but 
> > the settings are never saved; the drive status
> always says Compression: Off.
> > Does anyone have experience with this hardware
> with which they could 
> > enlighten me?
> > 
> > Thanks,
> > Lee Anne
> 
> -- 
> Larry Kingery 
>          Proofread carefully to see if you any words out.
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