Avago Technologies 3ware 9650SE-12ML (Channel) - Manual (Page 22)

Introducing the 3ware® SAS/SATA RAID Controller
10 3ware SAS/SATA RAID Software User Guide, Version 9.5.1
Figure 6. RAID 10 Configuration Example
RAID 50
RAID 50 is a combination of RAID 5 with RAID 0. This array type provides
fault tolerance and high performance. RAID 50 requires a minimum of six
drives.
Several combinations are available with RAID 50. For example, on a 12-port
controller, you can have a grouping of 3, 4, or 6 drives. A grouping of 3 means
that the RAID 5 arrays used have 3 disks each; four of these 3-drive RAID 5
arrays are striped together to form the 12-drive RAID 50 array. On a 16-port
controller, you can have a grouping of 4 or 8 drives.
No more than four RAID 5 subunits are allowed in a RAID 50 unit. For
example, a 24-drive RAID 50 unit may have groups of 12, 8, or 6 drives, but
not groups of 4 or 3.
In addition, RAID 50 arrays offer a higher degree of fault tolerance than
RAID 1 and RAID 5, since the array can sustain multiple drive failures
without data loss. For example, in a twelve-drive RAID 50 array, up to one
drive in each RAID 5 set can fail and the array will continue to function.
Please note that if two or more drives in a RAID 5 set fail, then all of the data
will be lost.