backup and disaster recovery

Scott H wrote:
>
> > From: George Toft <george@georgetoft.com>
>
> > Scott H wrote:
> > >
> > > I am working on methods for recovery of a
> > Linux
> > > server, and I wanted to run this by the group
> > for
> > > comments or recommendations, since I'm new to
> > > this. I have a server which acts as an email
> > > relay, storing no mail locally. It also
> > stores
> > > no other data, besides the configuration data
> > for
> > > its mail systems. I plan to set up an
> > automated,
> > > regular complete backup for it, but I was
> > also
> > > considering this: Say I have among my
> > partitions
> > > on this box:
> > >

> > > sda2    /
> > > sda3    /backups
> > > sda5    /var/log
> > > sda7    /var/spool

> > >
> > > Let's say I set up mirrordir to keep /backups
> > > (sda3) mirrored from / (sda2) maybe once per
> > > night or week. Then, if I manage to mess up
> > the
> > > OS (as I recently did, running tripwire and
> > > up2date at the same time - don't ask) and the
> > > machine won't boot, I wouldn't have to resort
> > to
> > > a rebuild and the tape backup. I could boot
> > the
> > > box to my LNX-BBC CD (or a Tom's root boot),
> > > change fstab to mount sda3 as / and sda2 as
> > > /backups, and reboot the box. As long as
> > > mirrordir hadn't yet copied whatever
> > corruption
> > > was in the OS, I should be able to boot and
> > go
> > > just as things were the last time mirrordir
> > ran,
> > > right????????? Better ways to do this?
> > >
> > > Scott
> >
> >
> > Hi Scott,
> >
> > Here's what I did at a web hosting company. I
> > had another drive
> > installed that mounted on /backup at midnight
> > (maybe later, depending on
> > server load at midnight). My backup script
> > copied /etc, /root, /home,
> > and /var. That was it. Everything else could
> > be rebuilt from the
> > master image.
> >
> > You could follow this same scheme (if using Red
> > Hat). If you hose your
> > OS, or the drive fails, reinstall using your
> > kickstart config file
> > (located in /root), then restore your data from
> > the other drive. I use
> > this method for my firewall, and I tested it
> > (bare metal recovery). The
> > scripts to do this are on my site
> > (georgetoft.com - linux - cool shell
> > scripts).
> >
> > Your idea is pretty slick, though - switch
> > partitions in fstab, reboot
> > and go. Keep in mind what happens if your
> > drive fails.
>
> Thanks for your comments, George. One other
> question: Is there any problem with using
> mirrordir for the entire / partition? I mean,
> there are undoutedly files that are open (and
> locked?) by the OS at all times. Might mirrordir
> not be able to copy these? Has anyone actually
> mirrored the partition mounted at / ?
>
> .
>
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Locked files? I've heard of them in Unix, but I have never seen one in
over 5 years of Unix/Linux use. The strategy I outlined worked well in
several Bare Metal Recovery situations, with the only loss being a few
hours of Apache logs. I used to copy mySQL files directly from
/var/lib/mysql - now I'm smarter and use mysqldump. Still, if any file
is open, it would be those - no problems encountered.

I would try to be smart about what I mirror. You don't need to copy a
file that hasn't changed, so I would run find / -ctime -1 to get a list
of files whose status has changed in the last day, and mirror those.
Next, you have to account for deleted files. I can think of a few
ways. The one I used was running find periodically and using diff to
see what is missing from the last time I ran it. Delete those files. I
synced 4 servers every 20 minutes this way. Fortunately, the
filesystems were small so find didn't kill the system.

George

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