SUMMARY: DDS3 (12GB DAT) Backwards compatibility

From: James Ashton (
Date: Thu Jul 17 1997 - 18:50:01 CDT


Does anyone with a new DDS3 (12GB native) DAT drive, especially one of
Sun's units, have any experience with reading older DDS2 (4GB native)
DAT tapes? We have a WangDAT 3400DX which does DDS2 plus hardware
compression. Will I be able to at least read compressed tapes written
by this drive? I have heard some FUD (fear, uncertainty and doubt)
spread concerning this so reports of success would be reassuring. If
backwards compatibility is advertised then I guess it has to work to
some extent but my main worry is that the hardware compression schemes
were (and perhaps still are) different and incompatible between
different manufacturer's drives.


Dave Mitchell reported success with reading a DDS2 tape written on a HP
drive using a Sun DDS3 drive although he didn't say whether the tape
used hardware compression. Apparently the DDS2 standard specifies the
hardware compression method so that, in theory, DDS3 drives should be
able to be able to read any DDS2 tape either with or without hardware

However Roland Grefer reported past problems exchanging DDS2 compressed
tapes between different manufacturers' drives and said that some
combinations of drives (Seagate, HP) were only `one way compatible'.
Ric Anderson, on the other hand, had never seen any such problems using
various drives (Seagate, HP, Sony).

People seem to agree that hardware compression was a major source of
drive incompatibility with the first generation of DAT drives (DDS) so
that there has to be great doubt about the ability of DDS3 drives to
read hardware-compressed DDS tapes. Non-compressed DDS tapes should be
no problem but I have no reports of any attempts.

In short, it seems that it would be prudent to arrange a trial to test
the compatibility of a DDS3 drive with any DDS2 or DDS tapes and drives
if you're going to rely on this functionality. This is especially the
case if, like me, you have a bunch of old tapes that use hardware

THE GLORY (David Mitchell) (Roland Grefer) (Ric Anderson)

James Ashton    		VK1XJA  		  System Administrator       	     Department of Systems Engineering
Voice +61 6 279 8675   Research School of Information Sciences and Engineering
FAX   +61 6 279 8688				Australian National University
Email   		   Canberra ACT 0200 Australia

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