[ On Wednesday, October 23, 2002 at 11:31:20 (-0400), Joshua Baker-LePain 
wrote: ]
> Subject: Re: Quick Multiple Tape Question
>
> Err, *can* dump/tar span a single *file* across tapes?  I'm not sure.  A 
> single filesystem -- sure.  But a file?

Yes, with dump you should be able to put large files on multiple tape
volumes.  Most versions of dump/restore can handle multiple volumes (and
they always could), and they shouldn't care if a file spans multiple
volumes, though it's been some time since I really tested this ability
in any implementation.

However most versions of tar/pax/cpio/afio should _not_ allow you to
span multiple tapes with a single file.  The formal definitions of
ustar, cpio, and now pax archive formats do not allow for multiple
volume support.

There are some proprietary formats (maybe even GNU Tar's) which might
allow spanning a file across multiple tapes.  The issue is that there
really must be a header on the second and following tapes, and normally
in the tar/ustar/pax/cpio formats a header always starts a new file.

So in order to use tar/pax/cpio/afio to archive files larger than a
single tape you either have to split large file first into just slightly
smaller than tape-sized chunks, or you have to create the archive on
disk, then split it into just less than tape-sized chunks and either
write each chunk to tape and very very very very carefully label the
tapes so that you can read the archive back in in the right order, or
then subsquently again use a version of pax or tar or cpio which does
support multiple volumes to put the archive chunks onto multiple tapes.

-- 
                                                                Greg A. Woods

+1 416 218-0098;            <g.a.woods AT ieee DOT org>;           <woods AT 
robohack DOT ca>
Planix, Inc. <woods AT planix DOT com>; VE3TCP; Secrets of the Weird <woods AT 
weird DOT com>