We have a 39 TB linux server (mdadm raid 6 15 3TB Drives) that has about 12TB of working data on it. Initially I wanted to create a snapshot system that only saved the data that was changed, much like a copy-on-write filesystem such as ZFS or what LVM does.
Unfortunately employees were already too far into using the XFS file system for me to start from scratch with LVM or a ZFS filesystem as it was going to be too troublesome/expensive to migrate all the data off the server and back on again.
As it is rsnapshot is creating an entire copy of the working data + diffs on the same raid as the working data is, thus filling up the raid twice as fast. Not only does this take up excessive disk space, it also eats up disk/io (I've mitigated this some with ionice -c3).
Is there a way to make it so that rsnapshot/rsync only uses hard links, and thus keeps around old files that might get deleted or moved but not necessarily a complete copy of the working data? It would basically behave more like a versioning software instead of backup software....