On 16 Jul 2000, at 19:25, Eric Lee Green wrote:
> Kevin Ernst wrote:
> > Also, I gather DDS drives are supposed to have more sophisticated
> > and reliable tape-and-head alignment mechanisms,
> Rather, since they are helical-scan devices, alignment is not as
> critical, since they aren't trying to lay down parallel tracks on the
> tape (which is where alignment comes into play). The need for absolute
I'm pretty sure I got that idea from some HP sales literature. =) I'm
glad someone better informed came along to set the technical details
straight.
> and applications programs). The theoretical disadvantage of helical
> scan devices is shorter tape life, due to the extra wear of having to
> go over a wide swathe of head at high speeds. It may be that helical
> scan tapes don't store as long either due to the tighter horizontal
> packing of bits. Both of these are so dependent on media material and
> composition, and tape head composition, that it's hard to make a
> tried-and-true rule here.
I had a sneaking suspicion that the life expectancy of DDS media was
a bit shorter, for reasons I couldn't explain. The information I
found on HP's Web site seems to support your theory: HP says their
DDS media will last through 2,000 passes or 100 full backups, and
retain data for 'ten years or more,' while their DLT media are
supposed to withstand 1,000,000 read/write passes (and retain data
for 30 years), and their Travan media are supposed to go for 10,000
passes and retain data for 20 years.
I'm not familiar with SLR, but the spec sheet for Imation's SLR data
cartridges rates them for 5,000 passes and a 10-year archival
lifespan.
I guess these are important things to keep in mind, but perhaps the
most tempting reason to select DDS media is because they're tiny and
cute.
> Note that this is not entirely true. Somewhere in the DDS line there
> was a media change similar to that in the QIC world, where the old
> tapes can be read, but not written, by the current drives. I'd have to
> check, but I suspect that DDS-4 tape drives cannot write DDS-2 or
> DDS-3 tapes, and absolutely cannot write DDS-1 tapes (which do not
This got me curious. I had access to a (Seagate brand) DDS-3 drive at
work, and I used it to write to DDS-2 tapes regularly without any
problems. But I seem to remember doing a test backup to a DDS-1 tape
out of curiosity as well, without incident. I always figured backward
compatibility among the DDS formats was just a firmware trick.
Seagate's current model, the Scorpion 40 (DDS-4), is able to read and
write all the way back to DDS-1 90 meter tapes, but not the 60m
tapes. HP's SureStore DAT40 doesn't support the DDS-1 recording
method at all, but supports reading of DDS-1 90m tapes. The Sony SDT-
10000 (DDS-4) looks like it supports reading/writing of all the
current and previous DDS formats. Sony seems to take that proclaimed
goal of backward compatibility very seriously. Maybe the others are
just shedding a layer of cruft.
The DDS-3 models from Tecmar, HP, Seagate, and Sony, however, all
appear to support reading and writing of DDS-2 and both DDS-1 90m and
60m tapes.
> > I'm actually thinking about chunking my Ditto Max as a paperweight
> > and getting a used DDS drive. Not that my Ditto Max hasn't been
> > working exceptionally under Linux (ftape-4.02)--it's just that the
> > media is too expensive.
>
> Don't forget the speed difference. Nobody has ever accused a Ditto Max
> of being fast. The wonder is that it works at all :-).
I picked up the Ditto Max for cheap (about 30 bucks) around the same
time Tecmar was taking over the Ditto line from Iomega and selling
them as 'Tecmar Ditto Max Pro's. The Iomega branded units were being
dumped out on Onsale.com. It was mostly a case of auction fever, but
it fulfilled my backup needs for a time. And it was fun to try to get
it working in my Linux box.
--Kevin
