[plug] re: disk backup

[Craig Ringer]

> I'm only interested in getting a backup nightly of the system and if it
> was possible to get a mirror image of the system this would be a bonus.

You could probably use LVM's snapshotting capability, then dd from the 
snapshot to the second disk. That's what I'm doing when I need to clone 
an entire filesystem for backups or testing on our new server here.

The downside is that you'll need LVM. Any rescue disks you want to use 
to access data on LVM partitions must also support LVM. Perhaps more 
importantly, there's no way to convert a normal filesystem on a 
partition to an LVM volume containing the filesystem. Instead, you have 
to dump the data to a backup, recreate the partition as an PVM volume, 
create a logical volume for the partiton, make a new filesystem on the 
logical volume, and restore the data.

Once it's going it's a wonder to work with though. I'm already so used 
to being able to take filesystem snapshots and allocate random-sized 
chunks of space for temporary purposes (need 10g for a reiserfs 
filesystem you'll use only for two days? No repartitioning required.). 
It's very nice to be able to expand (and shrink) filesystems on demand, 
too, without having to worry about shuffling partition start points 
around (the horror!).

I'm using RH8 on the new server here, and it comes with built-in LVM 
support.

Also, it looks like having the root FS on LVM is much more trouble than 
it's worth, at least from what I've been hearing. I haven't tried it myself.