Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!rutgers!ames!cit-vax!mangler From: mangler@cit-vax.Caltech.Edu (System Mangler) Newsgroups: comp.unix.wizards Subject: Re: Backup of a live filesystem revisited Message-ID: <1413@cit-vax.Caltech.Edu> Date: Sat, 3-Jan-87 00:54:32 EST Article-I.D.: cit-vax.1413 Posted: Sat Jan 3 00:54:32 1987 Date-Received: Sat, 3-Jan-87 03:38:10 EST References: <4760002@hpirs.HP> <1226@ho95e.UUCP> <7446@utzoo.UUCP> <5108@pur-ee.UUCP> Organization: California Institute of Technology Lines: 40 Summary: misconceptions about scheduler, /etc/dump In article <5108@pur-ee.UUCP>, davy@pur-ee.UUCP (Dave Curry) writes: > 1. Nice yourself down as far as you can. Like -20. A couple weeks ago a friend was converting a VMS BACKUP tape for me, and as we stood around while the TU80 slowly turned, I wisecracked about the TU80 on the nearby 4.3 BSD machine, which was turning just as slowly. He retorted that he had reverse-nice'd /etc/dump to -20, users be damned. Later, I found that the reverse-nice (mean?) was what made dump run so slowly. 4.3 BSD dump uses several processes, to overlap disk and tape I/O. Since it is I/O-bound, `usrpri' stays pretty close to PUSER+2*nice. If nice is more negative than -6, this will be a better priority than the flock wakeup priority, so the scheduler favors the current process instead of waking up the next tape writer. If nice is more negative than -14, the current process gets priority over disk I/O completions too. I think the I/O wakeup priorities are much too close to PUSER; PZERO ought to be changed to about 10. > 2. Modify dump (most of the mods are in dumptraverse.c) to > skip any inode whose mtime or ctime is greater than > spcl.c_date (time of the dump). This means that a full dump of the root filesystem will be missing /dev/console and /dev/rmt8. Not my idea of a useful backup... The modifications affect only pass IV. But that wasn't where dump was weak. An rm -r during passes I/II/III of stock 4.2 BSD dump will make restore dump core. 4.3 BSD /etc/dump skips deleted files and directories, allowing restore to get *much* further before dumping core, and it seems to have no problem with deletions during pass IV. The only thing I have to add to the 4.3 BSD sanity checks would be a warning message in dirdump(), since a deleted directory is still quite likely to make the dump useless. Don Speck speck@vlsi.caltech.edu {seismo,rutgers,ames}!cit-vax!speck