Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!rutgers!clyde!cbatt!ihnp4!houxm!ho95e!wcs From: wcs@ho95e.UUCP (#Bill.Stewart) Newsgroups: comp.unix.wizards Subject: Re: Backup of a live filesystem revisited Message-ID: <1226@ho95e.UUCP> Date: Tue, 16-Dec-86 17:42:19 EST Article-I.D.: ho95e.1226 Posted: Tue Dec 16 17:42:19 1986 Date-Received: Thu, 18-Dec-86 04:09:55 EST References: <4760002@hpirs.HP> Reply-To: wcs@ho95e.UUCP (Bill Stewart 1-201-949-0705 ihnp4!ho95c!wcs HO 2G202) Organization: AT&T Bell Labs, Holmdel NJ Lines: 29 In article <4760002@hpirs.HP> lkc@hpirs.HP (Lee Casuto) writes: >A few weeks ago I posted a request for information about a paper on >the backup of live filesystems. I also received lots of mail from >..... >>I hate to disappoint you, but no such paper exists. In fact I have gone >>out of my way over the years to make it as clear as possible that `live' >>dumps are NOT always going to work! The problem is that they usually do >>work, particularly if they are being used to extract individual files. >>But full incremental restores are likely to bomb out, and of course these >>are the ones that are most critical. >> Kirk McKusick There are two basic approaches to backups: programs that use the file system (e.g. tar, cpio), and programs that scrounge directly off the disk (dd, dump, volcopy, finc) File-system based programs can work on live systems as long as the individual files are not changing. They are slow but flexible, and do incremental dumps well. Unfortunately, they can't tell when a given file has been *removed*, and can get horribly confused if you play games with links or modification times between dumps. Disk-based backup programs are normally much faster, but are unsafe on live file systems; if nothing's being written at 3AM you may luck out. Disk-based *restore* programs are another story; you should expect terrible corruption if you use one on a live disk. Suppose someone was already using inode 443 when you try to restore it? -- # Bill Stewart, AT&T Bell Labs 2G-202, Holmdel NJ 1-201-949-0705 ihnp4!ho95c!wcs