HP Integrity rx4640 Server - Manual (Page 79)

Drive Arrays and Fault Tolerance
For any configuration except RAID 0, further protection against data loss can be
achieved by assigning a drive as an online spare (or hot spare). This drive contains
no data and is connected to the same controller as the array. When any other physical
drive in the array fails, the controller automatically rebuilds information that was
originally on the failed drive onto the online spare. The system is quickly restored to
full RAID-level data protection. (However, in the unlikely event that another drive in
the array fails while data is being rewritten to the spare, the logical drive will still
fail.)
When you configure an online spare, it is automatically assigned to all logical drives
in the same array. Additionally, you do not need to assign a separate online spare to
each array; you can configure one hard drive to be the online spare for several arrays,
as long as the arrays are all on the same controller.
Fault-Tolerance Methods
RAID 0—No Fault Tolerance
This configuration (refer to Figure D-3) provides no protection against data loss
when a drive fails. However, it is useful for rapid storage of large amounts of
noncritical data (for printing or image editing, for example), or when cost is the most
important consideration.
Advantages
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Highest performance method for writes
Lowest cost per unit of data stored
Maximum drive capacity for data storage (none needed for fault tolerance)
Disadvantages
Loss of data on the logical drive if a physical drive fails
Cannot use an online spare
Can only preserve data by backing it up to external drives
HP Smart Array 5300 Controller User Guide D-5
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