From owner-freebsd-questions Thu Sep 28 20: 7:38 2000 Delivered-To: freebsd-questions@freebsd.org Received: from mailhost01.reflexnet.net (mailhost01.reflexnet.net [64.6.192.82]) by hub.freebsd.org (Postfix) with ESMTP id B486C37B422 for ; Thu, 28 Sep 2000 20:07:26 -0700 (PDT) Received: from 149.211.6.64.reflexcom.com ([64.6.211.149]) by mailhost01.reflexnet.net with Microsoft SMTPSVC(5.5.1877.197.19); Thu, 28 Sep 2000 20:05:59 -0700 Received: (from cjc@localhost) by 149.211.6.64.reflexcom.com (8.11.0/8.11.0) id e8T37AS02823; Thu, 28 Sep 2000 20:07:10 -0700 (PDT) (envelope-from cjc) Date: Thu, 28 Sep 2000 20:07:10 -0700 From: "Crist J . Clark" To: j mckitrick Cc: freebsd-questions@FreeBSD.ORG Subject: Re: dump levels/incremental backups Message-ID: <20000928200709.J81242@149.211.6.64.reflexcom.com> Reply-To: cjclark@alum.mit.edu References: <20000929033448.A59083@dogma.freebsd-uk.eu.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Mailer: Mutt 1.0i In-Reply-To: <20000929033448.A59083@dogma.freebsd-uk.eu.org>; from jcm@FreeBSD-uk.eu.org on Fri, Sep 29, 2000 at 03:34:48AM +0100 Sender: owner-freebsd-questions@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG On Fri, Sep 29, 2000 at 03:34:48AM +0100, j mckitrick wrote: > I think I found enough scripts to help me choose a backup solution. But I > have a couple of questions. > > Is there some secret to what the 'levels' are in dump? dump(8) says, -0-9 Dump levels. A level 0, full backup, guarantees the entire file system is copied (but see also the -h option below). A level number above 0, incremental backup, tells dump to copy all files new or modified since the last dump of any lower level. The de- fault level is 0. Which means if you give a dump level of n, where n > 0, dump will check /etc/dumpdates for the most recent dump of at a level less than n. All files modified since that date are dumped. > What is the purpose of the 'Towers of Hanoi' number pattern? It is a trade between backup size and the number of restores that will need to be done to any given point. The series in the manpage is, 3 2 5 4 7 6 9 8 9 9 ... For size concerns, notice that each dump contains no more than two steps worth of changes. Now when we need to restore, say we have a problem at, 3 2 5 4 7 6 This point of the cycle. To restore the filesystem, we start with the level 0, then 1, then 2, then 4, and then 6. For a comparison, let's say we do a full dump, the "weekly" level 1, then just a level 9 for all intermediate steps, 9 9 9 9 9 9 9 9 9 9 ... Now, if we ever had to restore, we only need do, level 0, 1, then 9. However, note that the size of the dumps is increasing monotonically. That is, every file that was modified on that first step backup is _also_ backed up every step after (unless it got deleted). Let's look at the other extreme, 2 3 4 5 6 7 8 9 ... Now the size of each dump is minimized, but restoring is now gonna be a real hassle since you need to use every dump. > Is the tar incremental backup simply based on comparing the modification > times of the existing files to the stored ones? Don't use tar for backups, but I would assume so. What else would you do? -- Crist J. Clark cjclark@alum.mit.edu To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message