8
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. For example, Group A and
Group B can allow one Hard Drive in their respective group to be fail simultaneously.
2.3.4 Parity RAID (RAID 5)
Parity 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 compare to RAID 1 and RAID 10 and is the preferred method to reduce the
cost per Gigabyte for larger installations. Mirroring requires half of the capacity to protect the data whereas the above
example using three hard drives only requires a one-third of the capacity. The additional required capacity decreases as the
number of disks in the group increases (i.e., one-forth for four drives or one-fifth for five drives).
In exchange for protection, Parity RAID degrades performance for write operations. The write performance is slower
compare to RAID 0 is due to each write performed need to calculate the parity. However read performance will be
increase using Stripping Method.
2.3.5 Concatenation (Spanning)
The Concatenated mode combines multiple disks or segments of disks into a single large volume. It does not provide any
data protection or performance improvement but can be useful for utilizing leftover space on disks. Concatenation allows
the segments that make up the volume to be of different sizes.
2.3.6 Contiguous (JBOD/Single Drive/Segment)
The single drive is a virtual disk that can either be an entire disk drive or a segment of a single disk drive. Single drive is the
“Contiguous” configuration option when creating RAID Groups (or sets) in the SATARAID5 software.
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