Item Subject: cc:Mail Text
I've inquired a bit about the whole "head (mis)alignment" problem on the
DDS drives.  Following is the response from one source.  (Comments in
square brackets [] are mine.)

FWIW.

--Glenn Cole
  Software al dente, Inc.
  [log in to unmask]


Seagate (Conner) and HP owned this problem [but see below],
and to the best of our knowledge, it is something that has
only occurred in any meaningful frequency in the case of
their drives. Your questioner is correct about the issue,
and it relates specifically to those manufacturers drives listed
above whose drive heads shift off azimuth in such a way that the data
tracks are laid on the tape at too ablique an angle for a properly adjusted
drive to read them. You make your backups on the out of adjustment drive
and occasionally have to restore data - no problem. Your first notice of
the problem occurs when you take a tape made on one of these mechanisms to
another drive to read. Even the same make and model in proper alignment
can't read these tapes, and then, when that original unit finally gives up
the ghost and has to be replaced, all those tapes are essentially lost.

While there are similar problems that can occur on other tape platforms, I
believe that it has been largely solved with new drives from virtually all
manufacturers for quite a long time, and it's a problem that still does
rear its head occasionally. Moreover,  I believe that this single problem
did more to contribute to the bum rap that DAT took in the marketplace 2-3
years ago, than any other single problem, including [one company] knowingly
shipping bad 120MB DDS-2 media.

[then, in a follow-up msg...]

My reference to HP is heresay, as we
have not specifically handled HP DAT units on an integration basis or as
an OEM of HP. The source I'm referring to had the problem with both
Seagate (or Conner, as I can't remember the exact time frame of the
problem relative to the purchase of Conner by Seagate) HP DATs which had
both exhibited the same problem. He alluded to fairly widespread problems
within the world of HP's 4mm domain and I'm guilty of repeating it as if
it were my own experience. Subsequent to his experience we've been told
the same thing by several other sources.

The other caveat is that while the tapes made on an out of adjustment
drive, during the time that the drive is out of adjustment, will be lost
if that particular drive fails, the misalignment occurs over some period
of time so that we may not be talking about every tape ever made, and
conversely, those tapes made when the drive is slightly misaligned may
not still be readable when the drive drifts into gross misalignment.