[191] in Athena_Backup_System
[jco@direwolf.com: Re: Large environment backup solutions]
daemon@ATHENA.MIT.EDU (dkk@MIT.EDU)
Sat Feb 10 09:02:50 1996
From: dkk@MIT.EDU
Date: Sat, 10 Feb 1996 09:02:45 -0500
To: athena-backup@MIT.EDU
A list Brian and I are on has had some discussion of large-site backup
solutions in the past day or so. Here's a message in that chain which
gives an abstract view of a couple of aspects of backups systems
(after "Basic info", below). I found it useful. Maybe you will, too.
------------
To: valentin@pencom.com
Cc: bblisa@cs.umb.edu
Subject: Re: Large environment backup solutions
In-Reply-To: Your message of "Fri, 09 Feb 1996 18:13:12 CST."
<199602100013.SAA06235@psa.pencom.com>
Date: Sat, 10 Feb 1996 01:40:44 -0500
From: John Orthoefer <jco@direwolf.com>
Sender: owner-bblisa@cs.umb.edu
Precedence: list
X-Mailing-List: bblisa@cs.umb.edu
> The only complaint I've heard about BudTool is that it currently does not
> support 'snapshots'; that is, the file history is cumulative and will show
> files even if they were been removed before the last backup .
> However, that just means you may get more files than you need after a
> restore. That may or may not be important. It was not in our environment.
Are you sure this is what you mean? Because you can't do this without
replacing either your Unix file system or replacing the unlinks in all
software on your system.
What I've seen snapshot mean is that it will remeber which files you
had yesterday and which ones you have today. So you get an effective
backwards delta and a forward.
> Legato Networker apparently supports snapshots.
Not by your defintion of snapshot
-------------------------------------------------------------------------------
Basic info so you know what I'm talking about.
Forward Delta: only know what was added to a file system. So
you only know the what the file system looked like if
you had a union of ALL file systems since the last
level 0.
Reverse Delta: Diff the last backup with the current state.
Above file system backup: You look at the files through the
file system so anything that is funky about your FS
your backup sees the funkyness. However this is
typicaly very portable.
Below file system backup: Can avoid things that disapear based
on your filesystem view. But it means that the
software MUST understand the filesystem.
Backup weaving: Allows you to mix more than one filesystem per
tape at normaly the block level of the tape. This
allows you keep the tape running at full speed, and do
several FS at once.
So Tar, and cpio are abover the filesystem forward delta when used
with like find. Stock version of both just backup a higher archy.
Dump is below and forward delta. So it can catch things like files
with holes in them.
Legato, forard backup above the file system (with hole dectection).
Uses RPCs to move data between the source machine and the target
machine with the tape drive. Does Weaving at the block level.
Epoch-backup (or what ever they are calling it today.) Forward delta
with reverse file info. Above the filesystem with hole decection.
Uses rsh's to the remote machine and custom find/cpio to get the
files. Does weaving at the block level.
Bud tool. Is just a scheduler, it doesn't do any of the backups just
runs commands for you. So Bud tool is only 1/2 of Legato/Epoch, and
it's the missing 1/2 of Dump, tar, cpio.
Personaly I like Epoch the best. They did most everything right, in
my opion. Legato is good. I don't like the fact that they use RPCs
for comms.
Bias, I beta tested Epoch backup software. So I had some input early
on so that has some bearing on me liking it. On the downside when we
tried to buy it they couldn't even get us a quote. So we went with
Legato.
JohnO
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