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Server RSV-S5 User Manual
requires four drives. The drives are assigned as two sets of striped 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.
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. 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 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.
2.3.5 CONCATENATION
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.
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