[Info-vax] Backup TK50 tapes

[glen herrmannsfeldt]

Dennis Boone <drb at ihatespam.msu.edu> wrote:
> > While i'm sure there are more modern utilities to copy tapes, providing
> > you know the block structure of the tape, dd should copy it verbatim,
> > even if you have to write a script to read it block by block.
 
> NO NO NO!
 
> I love dd and all, but it THROWS AWAY BLOCK STRUCTURE and leaves you with
> a byte stream.  The block structure is important on tapes.
 
> Don't use dd to image tapes!

Yes, but he said copy tape, not image tape.

dd if=/dev/tape1 of=/dev/tape2 bs=1024k

should copy a tape as long as blocks are not greater than 1024k.
(and if they are, use a larger number).

For Unix tape I/O, read() reads one block, puts into the buffer what
fits, throws away the rest, and returns the length read.

Assuming we are talking about drives that can read/write variable
length records, dd should do it.

But the unix file system doesn't preserve the lengths in read()
and write() calls, so disk images won't have any.

-- glen