OK - So I've now got a couple of PC's backing up / syncing with the RPi attached to the USB hard drive. - I need to be able to quickly rebuild if this machine fails. - Since I originally created the hard drive filesystem with rsync, it seems reasonable to use this to backup to another machine on the network. The following command copies the filesystem, and I should be able to use this to recreate the RPi / USB disk system relatively quickly if it fails. I've also taken a copy of the SD card on a windows machine, so the rebuild procedure will be to recreate a new SD card, if necessary, add a new USB hard drive, and then use my rsync backup to restore the hard drive filesystem. - I really should test this!
~/weatherpi $ rsync -avxS root@weatherpi:/ ./backup --exclude "/My Documents"
The RPi with the hard drive seems to run 'Unison' very well - much more quickly than my old 'Buffalo Linkstation' at any rate. It initially took around 10 hours to copy >100Gb of data from one PC to the USB attached drive, but did so with no hiccups. I have then brought in another PC which only took about 20 minutes to do the initial synchronisation of the same data. - We have several PC's around the house, but all the user data - music, photos, documents etc is stored in /My Documents on each, regardless whether they are linux or windows. Then, I use unison to sync the data across the various machines by syncing with the Rpi box. For the Linux boxes, I can pretty simply rebuild from a CD. For the windows machine, I also keep a 'Macrium' backup copy on a portable USB drive. This strategy means that I have several copies of my data which should provide some resilience against a lost disk etc., and protection against failure on the windows system with a full byte copy of the disk. (I have tested recovery of this also when I've swapped disks in the machine).