4.2 dist tape

[Lyle McElhaney]

Ah, yes, making an exact copy of a tape with Unix. Its easy enough if its a
tar or cpio tape (provided you know that ahead of time), but what about
the Univac tape you just received with one label on it, giving the returnee's
address?

The easiest thing to do is to use dd, as the referenced article stated,
from one tape drive to another (with due regard to tape densities). If you
set the buffer size higher than any physical record size on the tape, dd
will make an exact copy of the tape file. We regularly copy tapes with
the command:

	dd if=/dev/nrmt0 of=/dev/nrmt1 bs=21000

Yup, it wastes space on a non-virtual machine, but almost any machine that
runs multitasking Unix (and has two tape drives) won't notice the
difference.

Now, the gentleman did have a valid gripe: why does the Berkeley setup manual
(and others, probably) wisely say "make copies of the tapes" and then don't
say how?  We certainly aren't all guri when we start, as many of us have,
becoming system admin's from a cold start.

I have a tape utility called ts that describes the file/record layout of
an arbitrary tape - so as I write a manual page I'll submit it to net.sources.
In addition, I also wrote a utility for making a tape copy on a system with
only one tape drive, as long as you have sufficient disk. Will post it too.

PS: Michael P., where are you?
-- 
		Lyle McElhaney
		(hao,brl-bmd,nbires,csu-cs,scgvaxd)!denelcor!lmc