huge file, spanning multiple tapes

Dan Nelson dnelson at
Thu May 1 15:03:23 PDT 2003

In the last episode (May 01), Jacques A. Vidrine said:
> I thought this would be an easy problem to solve, but I haven't found
> a decent solution after a bit of looking.
> I have a huge file, say 73GB.  I need to dump it to tapes that have a
> capacity of about 33GB each (but there is hardware compression, so
> there is no exact capacity).
> If the file would fit on a single tape, I'd just use good 'ole dd(1).
> I figured, heck, somebody is _bound_ to have written a simple utility
> that, say, reads from a pipe and writes to tape (or vice versa), and
> prompts for a tape switch when it hits end-of-tape.  But alas, I
> cannot find such a beast.
> Using dump, cpio, etc is not really an option.  I need to be able to
> later read the data from tape into a pipe without it hitting disk.
> Anybody have bright ideas?

How about tar?  That lets you specify a change-volume script so you can
change tapes when you're writing, and when you read the tape later you
can specify the --to-stdout flag so it doesn't write to disk.

If you can't have any headers, you can always tell dd to only write
33GB per tape: 

gzip < file | 
  dd of=/dev/ersa0 bs=64k count=$((33000000/64))
  echo "please insert next tape"
  head -1 < /dev/tty > /dev/null

	Dan Nelson
	dnelson at

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