We have on an old Dell 2850 with 4 SCSI drives, where we put a Hardware RAID5 on 3 disks and left 1 as spare. I dont remember exactly, but the RAID was setup in the BIOS, and when installing CentOS6, I just saw “1 drive”.
If it was software RAID, disk failure could be seen in /proc/mdastat, and I could simulate failure with mdadm.
As far as it is hardware ATM, how, at least, to know the state of the RAID array? (syncing, healthy,…)