[NMLUG] Disk-to-disk copying and booting

[matthew.mccleary at gmail.com (Matthew McCleary)]

Hello,

I am trying to implement a disk-to-disk backup scheme on a server.
It's not the ideal method (I would have chosen a tape backup myself),
but it's what I have to deal with.

I've got three 146 GB ultra-320 SCSI disks. They are installed in a
removable drive frame, though I do not think they are hot-swappable;
thus, when I install or remove one, I have to first take the machine
down.

One drive has a complete Red Hat 9.0 system installed on it, which is
essentially one large partition minus a small /boot partition and a 2
GB swap partition. The disk is designated /dev/sda.

I've been using dd if=/dev/sda of=/dev/sdb bs=1024k (and dd
if=/dev/sda of=/dev/sdc bs=1024k) to make a carbon-copy of sda onto
sdb (or sdc). I'm supposed to do a periodic backup of sda -- something
like once a month, rotating the two backup drives monthly. Thus we
would lose at most a month's worth of work, worst-case.

Here, I come to the problem. To make a new backup, I just run the "dd"
command again -- it doesn't care what's on the drive currently, and it
will even overwrite the partition map. Quite nice. The problem,
though, happens when next month rolls around and I want to make a new
backup.

If I take the server down and install one of the backup drives in the
frame, alongside the main drive, and boot it up, Linux freaks. It sees
duplicate /boot partitions (and actually, it would see duplicates of
all filesystems) and refuses to mount anything it sees a duplicate of.
I *think* it actually boots, but it does not mount all filesystems,
which of course will cause problems.

The only way I can think to get around it is to first delete the
entire partition map on the backup drive (essentially, destroy the
backup) and then install the blank backup disk in the frame, and then
boot. That seems to be the only way I can get Linux to boot normally.

Problem is, I don't have another server that I can install these
drives into -- and so the only way I can destroy the partition map is
by installing the drives in the very server I'm trying to back up -- a
"chicken and the egg" problem.

So, I'm appealing to you: what advice would you have for me to go
about solving this problem? A tape backup is (unfortunately) not an
option; due to policy I must do disk-to-disk backups.

Thanks,
Matthew

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<-- .\\ -->
Matthew S. McCleary, MCP
matthew dot mccleary at gmail dot com