I have a Dell 2600 with 6 drives configured in a RAID 5 on a PERC 4 controller. 2 drives failed at the same time, and according to what I know a RAID 5 is recoverable if 1 drive fails. I'm not sure if the fact I had six drives in the array might save my skin.
I bought 2 new drives and plugged them in but no rebuild happened as I expected. Can anyone shed some light?
Regardless of how many drives are in use, a RAID 5 array only allows for recovery in the event that just one disk at a time fails.
What 3molo says is a fair point but even so, not quite correct I think - if two disks in a RAID5 array fail at the exact same time then a hot spare won't help, because a hot spare replaces one of the failed disks and rebuilds the array without any intervention, and a rebuild isn't possible if more than one disk fails.
For now, I am sorry to say that your options for recovering this data are going to involve restoring a backup.
For the future you may want to consider one of the more robust forms of RAID (not sure what options a PERC4 supports) such as RAID 6 or a nested RAID array. Once you get above a certain amount of disks in an array you reach the point where the chance that more than one of them can fail before a replacement is installed and rebuilt becomes unacceptably high.
You can try to force one or both of the failed disks to be online from the BIOS interface of the controller. Then check that the data and the file system are consistent.
Direct answer is "No". In-direct — "It depends". Mainly it depends on whether disks are partially out of order, or completely. In case there're partially broken, you can give it a try — I would copy (using tool like ddrescue) both failed disks. Then I'd try to run the bunch of disks using Linux SoftRAID — re-trying with proper order of disks and stripe-size in read-only mode and counting CRC mismatches. It's quite doable, I should say — this text in Russian mentions 12 disk RAID50's recovery using LSR, for example.