I'm about to perform an experimental upgrade on my CentOS 5 server. If the upgrade fails, I want to be able to back out the changes to the filesystem. This scenario seems similar to the example in Section 3.8 of the LVM HOWTO for LVM2 read-write snapshots - but the example is rather lacking in the actual how-to.
How would I commit the changes, merging them back into the original partition?
How would I revert the changes, restoring the filesystem back to its original state? Should I assume that I'll need to restart several services, if not outright reboot?
Is it possible to snapshot only certain directories on a partition, or is it a partition-wide operation?