Kontron MSMSA104EX - Manual (Page 13)

MSMSA104EX / SATA Controller
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Disk Mirroring and Striping (RAID 10)
RAID 10 combines the features of both RAID 0 and RAID 1. Performance is provided through the use of Striping (RAID
0) while adding the fault tolerance of Mirroring (RAID 1). The implementation of RAID 10 requires four drives. The
drives are assigned as two sets of mirrored pairs.
The Data is written to RAID Group A, which is mirrored (RAID 1) and provides data redundancy. Alternating blocks of
data are then striped across another RAID 1 mirrored set, shown as Set B in the figure above. This provides improved
speed.
Under certain circumstances, a RAID 10 set can sustain multiple simultaneous drive failures.
Parity RAID (RAID 5)
Parity RAID, or RAID 5, adds fault tolerance to Disk Striping by including parity information with the data. Parity RAID
dedicates the equivalent of one disk for storing parity stripes. The data and parity information is arranged on the disk
array so that parity is written to different disks. There are at least 3 members to a Parity RAID set. The following
example illustrates how the parity is rotated from disk to disk.
Parity RAID uses less capacity for protection and is the preferred method to reduce the cost per megabyte for larger
installations. Mirroring requires a 100% increase in capacity to protect the data whereas the above example using
three hard drives only requires a 50% increase. The additional required capacity decreases as the number of disks in
the group increases (i.e., 33% for four drives or 25% for five drives).
In exchange for low overhead necessary to implement protection, Parity RAID degrades performance for all write
operations. The parity calculations for Parity RAID may result in write performance that is somewhat slower than the
write performance to a single disk.