From: utzoo!decvax!harpo!npoiv!alice!research!dmr
Newsgroups: net.unix-wizards
Title: dump
Article-I.D.: research.293
Posted: Wed Sep  8 03:44:21 1982
Received: Thu Sep  9 02:51:42 1982

Making the dump command restartable between tapes is a laudable
objective, but it is (if I remember how dump works) decidedly
non-trivial.  The problem is that dump does not decide in advance
how files are to be distributed onto the tapes.  It starts by
making several passes through the file system, deciding which files
are to be dumped.  Then it dumps the files themselves; however
the decision to change tapes is made dynamically.

Probably the minimal change would involve creating a file after writing
each tape that tells the last inode that was completely dumped,
and adding a dump option to read and believe such a file.
(Or just have dump print out the last i-number, and enter it manually
for the second dump.)   You do have to worry about how to decide, the second
time around, which files to dump.  I suppose this record could also
be saved in a file.

One simple change will vastly increase the reliability of multi-tape
dumps: have the command flush type-ahead, and insist on a full "yes"
answer when it is ready to change tapes.  This may already be in BSD
distributions.

I have seen in unix-wizards reports that dump gets badly boggled
on some "phase errors" -- files that have changed since the start
of the dump or during the dump.  This really shouldn't happen, and
should be fixable.   Since I have not seen the problem occur it may
be a problem only in some versions.

		Dennis Ritchie