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