Re: PS4100 in RAID 6 with 3 disk drives failed
That's because you are running RAID6 with one space. So two drives in the RAIDset failed as did the spare.
Sounds like you are running older EQL and drive firmware.
I would not stress that system unless you have a verified backup (or two).
I suspect that array is no longer under support contract? If not, then you will need to find a 3rd party reseller who has EQL drives that match yours. Standard OEM, or generic Dell drives will not work with EQL arrays.