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Path: utzoo!watmath!clyde!burl!ulysses!allegra!mit-eddie!think!ISM780B!tim
From: tim@ISM780B.UUCP
Newsgroups: net.unix-wizards
Subject: Re: Re: Help Me #1
Message-ID: <28500051@ISM780B.UUCP>
Date: Wed, 20-Nov-85 18:06:00 EST
Article-I.D.: ISM780B.28500051
Posted: Wed Nov 20 18:06:00 1985
Date-Received: Sun, 24-Nov-85 06:29:39 EST
References: <75@hadron.UUCP>
Lines: 23
Nf-ID: #R:hadron:-7500:ISM780B:28500051:000:755
Nf-From: ISM780B!tim    Nov 20 18:06:00 1985


I think it's like this:

	Each tape has at the start a list of inodes that were to be
	backed up when that tape was mounted, followed by as many
	files as would fit.

	If you are trying to restore the file with, say, inode 279,
	if you put on any tape before the correct one, it can look
	at the header, and see that inode 279 is one this tape OR
	A LATER TAPE.  It has to search the tape to see if it is
	indeed on that tape.

	If you put on a tape that is AFTER the correct tape, it can
	look and see immediately that it is not on this tape or
	any later tape.  Hence it is faster to search backwards.

At least, that is how some backup systems work.  I don't know any particulars
about bsd.

						Tim Smith
						ihnp4!cithep!tim
						ima!ism780!tim