Veritas-bu

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

2002-04-04 11:31:36
Subject: [Veritas-bu] Re: Implications of turning off s/w compresion?
From: ddunham AT taos DOT com (Darren Dunham)
Date: Thu, 4 Apr 2002 08:31:36 -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

Actually there are several different cartrige formats, but you don't see
many of the old ones around.  They used to be called CompactTape
followed by a roman numeral (and maybe some other bits), but now they
are called DLTtape.

The 7k and the 8k both use the DLTtapeIV for highest density and speed..
That gives 35G native on the 7k and 40G native on the 8k.  The 7k has
the option of using older media at the lower capacity and speed.  The
IIIxt will give 15G native and the III will allow for up to 10G.  The IV
came out years ago and is just about the only thing I've seen in the
past 4 years.  The tapes are color coded, too.  All the IV tapes are a
deep brown.  Others are black and tan, and cleaning tapes are white.

I don't know much about the DDS2/DDS3, so I can't say that they're
different or not.  As mentioned, the density format of a tape is set by
the a write starting at BOT.  You can override it later, but all blocks
currently on the tape must be at the same density.

Compression can be changed during the tape write (possibly only at file
boundaries though).  It is not set permanently by the BOT write.

DLT1 and DLT2 (and so on) in NetBackup do not correspond to any
particular device or tape type.  Since the OS is managing the
differences, NB doesn't need to know.

Instead, they are just there to mark certain volumes incompatible with
certain drives.  It's up to you to put them into the categories you
want.  If done properly, it lets you avoid trying to load a DLT8k
formatted tape into a DLT7k drive (where it will probably generate an
error).

The technical manuals are still online at quatum.com in PDF format for
more specifications.


-- 
Darren Dunham                                           ddunham AT taos DOT com
Unix System Administrator                    Taos - The SysAdmin Company
Got some Dr Pepper?                           San Francisco, CA bay area
          < How are you gentlemen!! Take off every '.SIG'!! >