User manual

Appendix A: RAID
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Disk Drives
Data
Mirro
r
Data Stripe
Figure 107. RAID 0+1 Striping and Mirroring of Two Drive Pairs
The data capacity is similar to a standard mirroring array, with half of the total
storage capacity dedicated for redundancy. An added plus for using RAID 0+1 is
that, in many situations, such an array offers double fault tolerance. Double fault
tolerance may allow your data array to continue to operate depending on which
two drives fail.
RAID 3 - Block Striping with Parity Drive
RAID level 3 organizes data across the physical drives of the array, and stores
parity information on to a drive dedicated to this purpose. This organization
allows increased performance by accessing multiple drives simultaneously for
each operation, as well as fault tolerance by providing parity data. In the event of
a hard drive failure, data can be re-calculated by the RAID system based on the
remaining drive data and the parity information.
The adjustable block size of the RAID 3 array allows for performance tuning
based on the typical I/O request sizes for your system. The block size must be
set at the time it is created and cannot be adjusted dynamically. Generally, RAID
Level 3 tends to exhibit lower random write performance due to the heavy
workload going to the dedicated parity drive for parity recalculation for each I/O.