[H-GEN] Linux backup tool of choice

[Greg Black]

On 2003-04-10, Russell Stuart wrote:
> On Thu, 2003-04-10 at 13:33, Stuart Longland wrote:
> > Fair enough, but they're better than *no* backup capabilities.  The
> 
> If the person who owns the business / operation understands that he is
> backing up until an unreliable piece of junk, that the drive will start
> writing random data to the tape without any warning or hint of trouble,
> if the person is prepared to restore the tapes on a weekly basis and
> compare the result to a known good copy to see if it still has any good
> backups, then by all means use it.

Even comparing the result is not a guarantee that the *next*
time you want to read the tape (i.e., when you actually need to
restore the data because your computer's home got burnt down) it
will still be possible to do that.  Maybe the drive you used to
write the tape (which was, of course, destroyed in the fire) is
different enough from all the other drives you can find so that
its tapes are not in fact readable by any other drive on earth.
Yes, this really does happen.

> If you provide a backup system that uses an unreliable drive,
> then do a verify that does a bit for bit check automatically after the
> backup.  This is often hard because file systems are rarely static for
> that long.  So instead use a better tape drive - one that reads the data
> it has just written using a separate head.

And even there, you're not out of the woods.  I had one drive
that did read after write verification and always reported that
the data was good.  It lied.  Fortunately, I had never believed
it and always tested the tapes.  The same drive could not read
its own tapes minutes after writing them.

As those who have been paying attention over the past year or so
will know, there is an almost infinite collection of horror
stories about tapes.  That doesn't mean you should not use
them.  It does mean that you should use the best drives you can
afford and that you should not have unrealistic expectations of
the ability of your backup system to save you.  It also means
that you should arrange for defence in depth.  Running regular
rsync's to other boxes on your LAN, for instance, is a good
idea.  I put important data on my laptop by running rsync under
cron every hour.  I always take the laptop with me so that it
won't get stolen or destroyed in the fire that destroys the rest
of the network.

But my principal backups are on tape, as they have been on all
my home Unix boxes for the last 25 years.  Despite its problems,
when properly managed, tape is very useful for backups.  Just
don't think you can trust it without taking lots of measures to
ensure that you really can.

Greg

-- 
Greg Black <gjb at gbch.net> <http://www.gbch.net/gjb.html>
GPG signed mail preferred; further information in headers.
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