Wirt wrote:
> That's not as bad as it sounds. DDS-2 tapes are readable by DDS-1
drives
> as well, so long as the contents of the tapes are not compressed.

Uh...  No, they're not.

One of my postings explaining DDS compatibility issues:
http://raven.utc.edu/cgi-bin/WA.EXE?A2=ind9512E&L=hp3000-l&P=R264

Note that my table in that old (1995) message is inaccurate for DDS-3
and higher: eg, DDS-3 media is 125m and DDS-4 media is 150m.  The
throughput rates may also be inaccurate (especially since newer drives
have commonly been faster than earlier drives even within a specific
level; eg, DDS-2).

Here's another table showing DDS media compatibility (using the
definitions from the above 1995 message):

       Recording mode:
              DDS-1      DDS-2 DDS-3 DDS-4
Drive: ----------------- ----- ----- -----
DDS-0   <60m   60m
DDS-1   <60m   60m   90m
DDS-DC  <60m   60m   90m
DDS-2   <60m   60m   90m  120m
DDS-3   <60m   60m   90m  120m  125m
DDS-4                     120m  125m  150m
       ----- ----- ----- ----- ----- -----
Capacity:    1.3GB   2GB   4GB  12GB  20GB  (Native; ignores
compression)

The recording mode used depends on the media inserted rather than on the
drive type.  This allows, for example, a DDS-3 drive to write on DDS-2
media in a manner readable by DDS-2 drives.

Note that the data density is a constant within each recording format.
Higher recording formats achieve progressively greater density.  DDS-4
had to sacrifice DDS-1 compatibility due to the disparity of recording
densities and techniques.

Note also that mixing significantly different media lengths on a single
drive is discouraged because the longer tapes are much thinner which
causes the tape to take on a different shape as it's held taut over the
tape head which in turn can cause the tape head to wear differently.
Ideally, you should pick one tape length (really tape media thickness
and pliability) and use it exclusively in that drive.  Trying to use
both 60m or shorter and 120m or higher tapes on a frequent basis in a
single drive is a really good way to make the drive develop reliability
problems. Some DDS tape specs (note the thickness):

http://www.hp.com/cposupport/information_storage/support_doc/lpg50108.ht
ml
http://www.fujifilmmediasource.com/specs/dds4spec.htm

P.S.  IMO, DLT is a far superior technology than DDS these days.  SDLT
and LTO/Ultrium both seem attractive choices when even higher capacity
and/or performance are needed.
--
Jeff Woods
[log in to unmask]
Quintessential School Systems

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