i want to set my Raspberry Pi up as an backup machine. That means that after some time (maybe every hour? any suggestions how often?) a program (maybe rdiff-backup?) automatically writes all the files to the pi. Therefore i need some hard disks for the pi. Currently i own one 500 GB Hard disk, and one with 320 GB. I'd like to combine them as a RAID 1, and with full disk encryption.
My question are now:
1) Would you suggest to buy two extra 1TB (or bigger?) Hard disks for a RAID 1? Or is it possible to just buy one 1TB hard disk and then use it together with my existing two hard disks in a raid 1?
2) Think you that the performance of the Raspberry Pi is sufficient for that task?
3) Has anyone done that already? If yes, which backup tool do you use?
1. With Raid 1, you will only be able to have an array as large as the smallest disk size.
2. It will perform poorly; but that may still be good enough for what you need.
3. I use rsync (but not on my Pi).
Moving to Other Architectures...
imo, the raspberry pi is unsuitable for backup purposes. It is way too slow (both I/O and CPU). The Ethernet port bandwidth is also shared with USB, adding more USB drives does not really make it any faster.
Consider connecting your HDD(s) directly to your desktop/laptop. That has a faster CPU for encryption and faster I/O channels.