Using RAID1 Mirror to back up a server?

[Stephen Anderson]

I consider a test of a RAID 1 to be part of normal admin duties (at
least every few years) after all these are 1750s. However, this
requires a proper backup of the server beforehand, so forcing a
rebuild of the RAID 1 without a proper backup is considered risky.

Warning: Risky stuff. Not for the feint of heart.

1.  First check the status of your RAID 1 (dellmgr). Also check the
drive information (within dell mgr) of each drive for any errors. May
be a good time for a consistency check? (This activity of checking the
RAID should occur often outside of backup activity.)
2. Backup your server with whatever method that you normally do. (e.g.
rsync or whatever)
3. Restore a "test" system from your backup. Test your newly restored
system. (Is the system a proper replacement for your production
server?)
4. After you are satisfied with the results of steps 1 thru 3, pull
the second disk of the RAID 1 mirror while the system is booted into
the OS (that is the risky part). Place this disk aside, and insert a
new disk in the second slot. The RAID should rebuild. Do not do
anything with the removed disk until you are satisfied that the RAID 1
is okay (repeat checks in dellmgr).
5. Now you can create a system from the disk that you removed. Power
down a system that has a RAID 1 two disk config. Place the disk that
you removed earlier in the first slot and leave the second slot of the
RAID 1 empty. Boot the server. When the server is running place a disk
in the second slot, and the RAID should rebuild.


On 3/14/07, Kuba Ober <kuba at mareimbrium.org> wrote:
> On Wednesday 14 March 2007, cwilson at filertel.com wrote:
>
> > 2 servers work together and are "Online."  2 servers are supposed to be
> > back up.
> >
> > The problem I have, other than being a complete Linux N00b, is that the
> > backup servers are missing about a year of updates and patches.  The
> > backup Boot server is supposed to look exactly like the online Boot
> > server, and the backup database server should like just like the online
> > database server.
> >
> > I am told that there is a process in which I can pull one of the mirror
> > drives out of the production servers (online servers) and use them to
> > build up a new mirror on the backup servers.
> >
> > Is this feasable?
>
> It's crazy.
>
> rsync should do the job. If acl's are used, you may need to use latest rsync
> and compile it yourself. If selinux is used, I have no clue what's needed to
> preserve whatever metadata selinux needs. Maybe rsync uses xattr and that
> would preserve both acls and selinux stuff -- you'd need to find out about
> that. Since it's a very old system (RHEL 2.1), I doubt it has selinux, and I
> don't know if it'd use acls anyway.
>
> Make sure that you do rsync -ax, so that it preserves everything and stays on
> the same filesystem without trying to mess with /proc etc. You'd be obviously
> doing the sync to the root directory on the offline server, and you'll need
> to write your /etc/rsyncd.conf accordingly. Make sure you're in single user
> mode on the target (offline) server, and start the network (service network
> start) if it didn't start by itself.
>
> On the online server, you'll do this:
>
> 1. Install rsync
> 2. Prepare /etc/rsyncd.conf *as if it was the offline server!*
> 3. chkconfig rsync on
> 4. Make sure that relevant firewall port is open.
>
> On the offline server:
>
> 1. Install rsync
> 2. Copy /etc/rsyncd.conf over manually from online
> 3. chkconfig rsync on
> 4. Make sure that relevant firewall port is open.
>
> Then back to the online server:
>
> 1. df to find out the mounted filesystems (disk-based ones!)
> 2. rsync / rsync://offline.server.address/module-name
> 3. rsync /var rsync://offline.server.address/module-name
> 4. and so on (above I've assume that you have /var mounted separately)
>
> Cheers, Kuba
>
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