User guide

Hard Drive Arrays E-9
RAID 1 always requires an even number of drives. To improve performance in
configurations with more than two drives, the data is striped across the drives.
If a drive fails, the mirror drive provides a backup copy of the files and normal
system operations are not interrupted. The mirroring feature requires a
minimum of two drives and, in a multiple drive configuration (four or more
drives), mirroring can withstand multiple simultaneous drive failures as long
as the failed drives are not mirrored to each other.
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Figure E-7. Drive mirroring stores an identical copy of the data
No Fault Tolerance (RAID 0)
RAID 0 provides no fault tolerance. This level of RAID stripes data across all
the drives of the array, but it does not incorporate a method to create redundant
data. Therefore, if you choose this RAID option for any of your logical drives,
you will experience data loss for that logical drive if one physical drive fails.
However, because none of the capacity of the logical drives is used for
redundant data, RAID 0 offers the best processing speed and capacity. For this
reason, you may consider assigning RAID 0 to drives that require large
capacity and high speeds but do not contain critical data.
Before choosing the RAID 0 option, consider the following:
■ Disk failure will result in data loss for all RAID 0 logical drives.
■ You cannot assign an online spare to an array containing a RAID 0
logical drive.