RAID 50, also called RAID 5+0, combines the straight block-level striping of RAID 0 with the distributed parity of RAID 5.
A minimal RAID 50 configuration requires at least 6 drives.
Characteristics & Advantages
RAID 50 improves upon the performance of RAID 5 particularly during writes
Provides better fault tolerance than a single RAID level.
Disadvantages
Implementation is very expensive
Compared to RAID 5 parity overhead, the RAID 50 overhead is the multiple of the number of RAID 5 segments
Failure of two drives in one of the RAID 5 segments renders the whole array unusable