When you say "a file it cannot read", what kind of errors are you getting?
RSR errors?

The main thing is you should NOT be getting files TSM cannot read.
However, we had DLT drives in a 9710, and had many similar problems.

Collocation causes so much start/stop activity, with many tiny appends, the
DLT drives just couldn't handle it.
Got a lot of "false" cleans on the DLT drives, and tapes that couldn't read
back, lots of RSR errors.

Had to turn off collocation because of it; the drives and media get much
less stress that way,
but it caused our restore times to be too long.
Eventually replaced the DLT drives with 9840's, they handle start/stop and
appends OK.

My opinion and nobody else's,

Wanda Prather