1/2" tape cleaners?

From: der Mouse <mouse_at_Rodents.Montreal.QC.CA>
Date: Sun Oct 24 16:26:36 2004

>>> Linux has the Unix-standard mt command, too, which allows setting
>>> the blocksize the system device uses, either explicitly or to a
>>> variable blocksize.
>> Ah... I have never used that facet of 'mt' before
> You dont need 'mt' (under any UNIX system) to read non-local tape
> formats.

"Under any UNIX system"? Have you tried them all?

> It doesn't even work that way: by using 'mt' to set the block size,
> you only set its *reblocking* factor.

This depends on the drive hardware and the driver. Some tape drives
really do have fixed hardware block sizes. Even if setting a variable
block size just causes the drive to do reblocking of some fixed on-tape
block size, it still looks like a variable size block to the host.
(Indeed, a classic half-inch tape can be thought of as having a fixed
one-byte block size which is reblocked in hardware according to control
information on the tape, though that's not a terribly useful POV.)

> where usually, a length of 0 indicates an EOF (end of logical file,
> aka "first tape mark detected") or EOT (end of tape, aka "second
> consequtive tape mark detected") situation.

If you are using real half-inch tapes, detecting EOT is hard. I've run
into tapes with a dozen consecutive tape marks and data after them;
with some hardware, if you keep reading you'll eventually run off the
*physical* end of the tape - I've done it, and on the less friendly
drives it's a mess to re-thread the tape enough to rewind it onto the
original reel.

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Received on Sun Oct 24 2004 - 16:26:36 BST