HP 6-Port SATA RAID - Manual (Page 20)

Appendix D: About RAID 20
RAID 50
This dual-level RAID type is created by using two or more equal-sized RAID 5 arrays to create a RAID 0 array.
The top level RAID 0 array shares the load among the second-level RAID 5 arrays, improving both read and write
performance. Parity (Pan or Pbn), used in the second level RAID 5 arrays, provides efficient redundancy.
Figure 7 A RAID 50 array