Adaptec SAS/SATA/SCSI RAID Controllers - Manual (Page 75)

Appendix B: Understanding RAID ●
75
RAID 50 Arrays
A RAID 50 array is built from six to forty-eight disk drives configured as two or more RAID 5
arrays, and stripes stored data and parity data across all disk drives in both RAID 5 arrays. (For
more information, see
RAID 5 Arrays on page 73 .)
Note: Because they support four disk drives only, the Adaptec 2420SA RAID controller can’t
support RAID 50 arrays.
The parity data provides data protection, and striping improves performance. RAID 50 arrays
also provide high data transfer speeds.
Drive segment size is limited to the size of the smallest disk drive in the array. For example,
three 250 GB disk drives and three 400 GB disk drives comprise two equal-sized RAID 5 arrays
with 500 GB of stored data and 250 GB of parity data. The RAID 50 array can therefore contain
1000 GB (2 x 500 GB) of stored data and 500 GB of parity data.
In this figure, P represents the distributed parity data.
RAID 5
B
RAID 50
Logical Drive
=
1000 GB
plus Parity
RAID 5
A
Each RAID 5 Logical Drive has
500 GB Data Storage
250 GB Parity Data
Drive 1
250 GB
Drive 2
250 GB
Drive 3
250 GB Drive 4
400 GB
Drive 5
400 GB
Drive 6
400 GB
1, 5, P 3, P, 9 P, 7, 11 2, 6, P 4, P, 10 P, 8, 12
Total Unused
Space = 150 GB