Subject: Re: Amanda backups: gtar or dump?
To: dustin sallings <>
From: Chris Jones <>
List: current-users
Date: 10/26/1998 12:09:02
>>>>> "DS" == dustin sallings <> writes:

DS> 	Oh, it'll also use kerberos IV.  I never got it working with
DS> 5, though (didn't try too hard).

I did.  Or at least, I got it working with a K5 server running with
the K4 emulation stuff.  I don't remember exactly what was involved,
but it seems like it was pretty straightforward.

My $0.02 on dump vs. gtar:  They both suck.

dump:  If you're doing a dump of a live filesystem, it's quite
possible to produce an unusable dump.  The simplest way I've seen to
achieve this is to delete a directory tree after the dump has started,
before it finishes.  When dump hits it, it somehow produces a dump
that is not usable.  In other words, it doesn't just mess up the
directory tree you deleted; it messes up lots of other files, too.  I
assume the loss isn't total, but it *is* major.  So, IMHO, the only
safe way to use dump is on an "offline" filesystem, where you define
offline to mean whatever you think is appropriate.  I think Sun's
veritas filesystem had the right idea here, though I've never used
it.  It supposedly lets you make a mirror of a live filesystem, and
then stop mirroring.  At that point, you've got a snapshot of a live
filesystem, which can then be backed up via whatever means you like.

gtar:  A friend who wrote a tar clone told me that the tar standard
isn't really very standard; I don't know exactly what this means, but
I do know he was working off the POSIX tar stuff.  Tar can also be
slow.  Tar changes the atime on files, so users show up as having read
their email at the last backup time.  I've heard (unsubstantiated)
reports that tar crashes when it tries to deal with certain strange
filenames, and that it hangs on files that have certain types of locks
on them.

Really, I'm not sure that there is a good way to backup a live
filesystem.  You want a tool that operates below the filesystem level,
but which is immune to (or at least compensates for) changes to the
filesystem that occur while it's running.  I'm not going to claim to
know how to do this.


Chris Jones                                
           Mad scientist at large          
"Is this going to be a stand-up programming session, sir, or another bug hunt?"