raid - Dell PERC H700 and 8 disk slots : what are my options to increase disk fault tolerance?

We've got a Dell PowerEdge T510 which has 8 disk slots in the front. It is currently utilising 6 of these slots, and the disks are controlled by a PERC H700 controller. The disks are currently running in the following configuration

• 2x500GB in RAID 1 (OS partition)


• 4x2000GB in RAID 5 (file storage partition)

Considering that this server is our domain controller which hosts the Active Directory, I'd hate to see the server go down due to disk failures. Thus, I'd like to upgrade the server with disk fault tolerance in mind (and not storage capacity or speed). However, I'm not quite sure what my options are.

I was thinking of simply adding 2 more 500GB disks and convert the OS partition from RAID 1 to RAID 6, as this partition would be the most critical. We do have backups of important data on the RAID 5 partition, and it can be recreated within about 24 hours, but the OS partition would need more as it would require me to do a complete restore of Windows Server including Active Directory from backups.

However, I still acknowledge that RAID 5 has the habit of "acting up" during rebuilds, and I would of course love to convert this one to RAID 6 as well. However, the chassis only has 8 slots.

What are my options to secure this system with regards to disk fault tolerance?

Thanks!

UPDATE:

• Even though not stated initially, we do of course keep backups of the OS partition (Active Directory). I know that RAID is not a backup system.


• A second DC is not an option due to budget and licensing restrictions on SBS 2011.

The question was aimed towards my disk fault tolerance options. In other words, I'm looking for a good RAID setup.