My house lost power and the system was improperly shut down. Usually when this happens I just have to do a parity check when starting the array back up. I had a UPS but it died, probably time to get a new one. Anyway, this time upon boot all my drives were unassigned. I did some searching on the forum, ran a checkdisk on my flash drive, it's fine. The .dat file used to house the assigned drives however was 0 bytes.
I deleted the file and went to start assigning the drives back, but noticed I was missing one. Looked at the syslog and found that one drive was failing to respond. It detected something was there, but first tried 3Gbps, then 1.5Gbps, then it timed out. So looks like I lost a drive in the power failure as well.
Now, I have an extra drive I can put in. I slid it in and it was detected no problem, however because it was an improper shut down my parity isn't trusted. I know the fileserver wasn't doing anything at the time because it was in the middle of the day and no one was home, so I personally think the parity is fine. Do I put in the new drive, and just hit rebuild? I'm worried that if I do that the parity drive may be overwritten with the blank drive instead of the other way around.
What are the correct steps to go through to prevent any data loss? Thanks guys.
Update: I was able to borrow a 2TB drive, rebuild with it, and then expand with my spare 4TB. The server is now up and running. Many thanks to johnnie.black and RobJ!