Backing up a few servers isn't that hard. I managed the backups(and pretty much re-wrote the entire system) at a VPS provider. We essentially went in and back

Backing up a few servers isn't that hard. I managed the backups(and pretty much re-wrote the entire system) at a VPS provider. We essentially went in and backed up every LV found that didn't match certain patterns. You definitely want some sort of snapshot functionality to help you out and lvm provides that to you. It also makes it a piece of cake to add another server to the backups; as long as it has LV's they will get backed up. There was of course a lot of logic to handle edge cases, DRBD, ntfs, alerting, rsync includes/excludes, etc. The trouble comes when you need to backup an entire business, including all the VPS's, every night. The shear volume of files and the LSTAT's was killing. I remember when we crossed the number of files we had enough RAM for XFS to cache the metadata for and performance started to plummet. In the end we ended up moving to ZFS backup boxes, tons of RAM, rsync inplace, and snapshot send/receive to replicate between data centres.