Raid - How do I know which discs will be overwritten?

oh boy. This is bad.

I'm not sure how much you know about RAID, so I advise you to look at the wikipedia article to get a feel for the different RAID configurations.

Disks on servers have no business being in RAID0 period. If one disk dies, the data on both is lost. I ASSUME that your IT guy had at least two functioning brain cells and used something more sensible such as RAID1, RAID5, RAID6, or RAID10.

If two disks are dead, you may be SOL. Without knowing more about what organizational structure your server used it's impossible to tell.

markings 0 through 5 implies 6 drive bays. I assume that all are populated.

If the first two are used for the OS, they were hopefully mirrored (RAID1). You didn't replace either of them so if that's the case, you're good to go regardless of what happens.

The following 4 are what concern me. If those disks are in RAID10 (unlikely, but who knows) then you MAY be okay with two disk failures provided that the two disks that failed are on opposing stripes. I would assume that disks 2 and 3 are mirrored copies, and disks 4 and 5 are mirrored copies. If this is the case, then replacing disks 3 and 5 should allow the RAID10 to be rebuilt from disks 2 and 4. If this is not the case, meaning that disks 2 and 4 are mirrored copies, and disks 3 and 5 are mirrored copies, then the RAID is gone.

If the 4 disks are in RAID5 (more likely than RAID10) then the raid is gone. RAID5 allows for an array of n identical disks to have the combined capacity of n-1 disks while being able to tolerate a single disk failure. If two disks fail, RAID5 cannot be rebuilt.

If the 4 disks are in RAID6 (unlikely with only 4 disks) then the raid is okay. RAID6 is identical to RAID5 except that it has the combined capacity of n-2 disks while being able to tolerate two simultaneous disk failures. If three disks fail, RAID6 cannot be rebuilt.

If the 4 disks are two separate RAID1 (implying that there are a total of 3 RAID1 configurations in the machine), then both are okay assuming that disks 2 and 3 are mirrored, and disks 4 and 5 are mirrored.

If the 4 disks are indepedent, then disks 3 and 5 are gone.

When you boot it up it will give you a status as to which RAIDs are online, which are offline, and which need to be rebuilt. RAIDs that need to be rebuilt can be used, but may suffer degraded IO performance while rebuilding. Good luck.