I am in the process of setting up a RAID card on an NT 4 Server. We are going to run 4 18gb drives in a RAID 5 and 1 hot swap. We are curious to know if we put the OS in the array, will the system continue to run if one of the drives fail or will it fail and not be bootable until the array is reconstructed. Any information will help. Thank you.

the OS is inside the RAID "container", if apply RAID5 not avoid system down, then there is no reason we go for RAID array. To answer your question is "YES" the system will perform as normal but the performance will slow down until you put back the drive & system will generate back the block. Before you let your server online, please do a test on remove one of the drive, make sure your RAID array is working.

In a 4 disk RAID 5 array, you can have a drive go offline, and the OS will still stay up and running, the HOTSPARE drive will be used to rebuild the off-line drive until you can fix it. If you have two drives go offline, then it will crash you OS, but you will still be able to rebuild it. As long as you have a good hotspare on standby, your OS will stay stable.