I have never had an actual drive failure on my NAS box nor have a had to rebuild my RAID. I did set the system to manually rebuild the Raid, not automatic.
Also, do you have your NAS on an UPS? I found a great deal for an UPS at Best Buy two weeks ago for $40.00. It has the capacity to run the NAS for over 90 minutes, much longer than any of my computers will last during a power failure. So this results in no network traffic well before the NAS power source fails and hopefully maintaining my data integrity.
I guess what I'm asking is, do you have an UPS for the NAS and it lost the RAID, or are you on regular power, unprotected where a power drop could have caused a data issue?
Also you will here this a lot, always backup your data to a long term storage medium. I backup my computer to my NAS so if my computer dies, I have the NAS. If the NAS dies, I have the computer. Also since I store photos on the NAS, not on my computer, I put those files every month or two on to a DVD-R media.
If you are going to attempt to backup all your data from the NAS drives to a seperate hard drive, if you have a large amount of data, it will take a long time to move that data from the NAS to another drive, possibly days. I just backed up my entire NAS (725 GB) to a single 1 TB drive. It took 2 days to copy everything because the NAS has a slow throughput. You can mount one of the NAS drives into your computer, mount it, and copy it a lot faster. I wasn't in a hurry but maybe next time I'll opt for the faster method.
-Joe