Stefan Held wrote:
Am Mittwoch, den 10.12.2008, 14:29 -0600 schrieb Les Mikesell:
I'm not sure how practical that would be unless you could still mount
and access the updated version after reverting. Suppose you've done
several days work before you trip over the showstopper bug that makes
you want to revert. Or the update makes format changes that aren't
backwards compatible in files on other partitions?
This is more than practical :)
To be honest, the solaris guys are doing this recently. Take a snapshot,
apply the updates. If something is wrong you can move backwards and
forwards in the snapshots for the root partition.
I'd go for an option to install a spare matching partition for the
system and have updates always rsync the previous to it before changing
anything (both partitions always mounted, no lvm magic) but even that
doesn't cover everything that can go wrong.
This solution would be best with splitting /home into a own lvm
partition. I never heard of a system update breaking something serios
in /home :)
I think that means you've never tried running multiple versions with an
nfs mounted home. All sorts of things twiddle their dot-files with
changes that older copies don't like. So once you have run the new
version of a program you may not be able to go back.
Your solution would use to much space in my opinion.
Disk space is cheap in most cases - and regardless, an LVM would have to
have space for the snapshot and it's cheaper than maintaining a separate
test machine or VM image. And as an option, anyone who didn't want it
wouldn't have to. The main downside I see is that you'd have to decide
up front how big the system can grow and allocate 2 of them.
I do think it is better to focus on how to avoid breaking important
machines in the first place - and that necessarily involves breaking
more unimportant ones, but this could be another safety net.
--
Les Mikesell
lesmikesell@xxxxxxxxx
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