Number of failed disks allowed by RAID 2.0+.
The number of failed disks allowed by RAID 2.0+ depends on the RAID level.
RAID 3 and RAID 5 only allow one disk to fail.
RAID 6 and RAID 50 only allow two disks to fail.
RAID 10 only allows N disks to fail (RAID 10 is composed of 2 x N disks).