DAT's - gotta love 'em, gotta hate 'em...

One bad problem with DATs , especially DDS2s, is that the heads tend to drift
out of alignment long before they give a failure. This means that your heads
have gotten out of factory alignment - not so bad that the tape drive errors,
but bad enough that another tape drive will not read its data. This was really
bad with the DDS2s - a client would finally have a drive go fulltime bad (finally
drift out of tolerance) and then not be able to read their tapes when a new,
factory aligned drive is installed, and this could be months worth of backup
information.

I have found that sometimes going to a higher density drive will allow a little
more tolerance, ie: using a DDS2 tape in a DDS3 drive can sometimes recover
the data. It has been procedure around CTS for quite some time to replace all
DDSs and DDS2s DATS with DDS3s for just this reason. The higher density
DDS3 does not seem to tolerate drift as much as the earlier versions, thus
DDS3 tapes tend to not have this problem as bad as the DDS, DLZ and DDS2.

A tape drive does not mark a tape as bad when it is encountered - how could
this work with the write tape disabled - it does however flag the drive for
cleaning when this is encountered too often. Watch for this recurring error, it
is a clue. If the cleaning does not fix the problem, or it re-occurs frequently,
then this is a sign that the head is drifting and you may be losing all integrity
in your backups regarding information recovery on another tape drive. I have
seen this happen on DR tests - known good tapes from an online drive cannot
be read on the DR system for just this reason - incompatibility between the
drives.

Quick fix - two tape drives in house - write on one, verify on the other, or
alternate the read and write drives. Much like verifying backups, this is
usually the leason you wish you had learned about ten minutes ago...

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