I like the idea of a discussion about the advantages and disadvantages of RAID arrangements.

Another solution to the two hard drives backing up might be to use Raid 0 (striping).  This does not allow redundancy but it does let you combine the drives so the system sees them as one drive.

I have set up an Ubuntu 8.10 server with a 250gb boot disk and 4 1tb SATA hard drives in Raid 5 (using software Raid).

I trust Raid 5.  We have a mail server that has Raid 5 and twice we have lost one of the drives and been able to get the new drive, put it back into the Raid and let it rebuild with no down time except the time to put the new drive in (20 minutes). 

Something else I learned about Raid 5 and 6 from my research into a Blade server and a SAN is that the more drives you have in your Raid it increases that bandwidth (throughput) of the data letting everything work faster.

I don’t necessarily consider the loss of the BackupPC data a catastrophe.  I could see how it could be for someone that really wants to keep archive copies of backups.  If we have a total failure of BackupPC we would rebuild it and start backing up again.  I guess the worse scenario would be something that would not only hurt our BackupPC server but also damage several other servers at the same time. 

The question comes down to each individual and how much time can you afford to rebuild the data.  Is that downtime worth the extra money to put in more redundancy in the drives, offsite solutions or clustered servers.

There are so many options but they all have a positive and a negative and I don’t think any solution, no matter how much money you have, is 100% failsafe.  The odds of not being able to recover may be small but it is still there.