[H-GEN] Tape Drives

James Lever jamver at adams.humbug.org.au
Mon Jan 7 17:08:37 EST 2002


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According to Michael Anthon (on Tue, Jan 08, 2002 at 07:29:17AM +1000):
> Something I just thought of... do all drives (of the same form factor of
> course) use the same compression algorithm?  If I write on a Sony DDS4 with
> hardware compression, can I read it back on a WhoFlungDung drive?  Never
> even really thought of this before...

This should work consistently because if I understand it correctly,
everybody who manufactures DDSx drives are members of the DDS Manufacturer
Group (http://www.dds-tape.com/) and are working to the same standard.

One thing I did notice not mentioned earlier is that if you put a DDS3 tape
in a DDS4 drive, the drive will work in DDS3 compatibility mode writing 
the tape as if it was a DDS3 drive so that it can be restored on a DDS3 unit
later.

Another warning, all drives can read tapes of previous formats (DDS4 >=
DDS[1-3), however IIRC, a DDS4 drive can no longer write DDS1 format
tapes.

Regarding compression turning on/off, it doesn't appear to have been
mentioned, but for those who aren't in the business of working with tapes
to turn it on/off is strictly dependant on whether you're writing to the
correct device file. this can easily be deteremined by looking up the
tape driver man page on your system of choice (via man mt as it's different
under each OS).

Oh, and personally, if you really wanted to do a large scale local gzip of
your data in a pipeline while backing up, it's very worthwhile making sure
you have a large buffer ahead of the gzip to keep data streaming nicely to
the tape drive.  If I personally wanted to do software compression on the
fly, I would probably either use gzip (-5) or gzip -1 piping through dd with
blocksize specifications and also use the hardware compression on the drive
as this is supposed to be fast enough that it has no performance loss to
avoid tape stop/start issues.

Food for thought.

cheers,
James

-- 
http://www.visac.uq.edu.au/people/jamver/index.html#sigs


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