User guide

Understanding Drive Arrays D-9
No Fault tolerance (RAID 0)
RAID 0 does not provide 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 complete 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 speed but does not contain critical data.
Before choosing the RAID 0 option, be sure to 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.
Online Spares
During configuration, Compaq recommends assigning an online spare to
further improve your system’s fault tolerance. An online spare (sometimes
called a hot-spare) is a drive the controller uses when a drive failure occurs. If
a drive fails, the controller rebuilds the data that was on the failed drive onto
the online spare. The controller also sends data that it would normally store on
the failed drive directly to the online spare.
The online spare improves the overall system fault tolerance by automatically
replacing a failed drive and quickly restoring the system to full RAID fault-
tolerance protection.
NOTE: During the time the system is operating in interim recovery mode with the failed
drive, the system is vulnerable to an additional drive failure just as it would be without a
spare drive installed.
You can install up to five online spares for each Smart Array 431 Controller.
To provide an online spare, you must have at least one installed but unassigned
physical drive and the system must be running some type of fault-tolerance
method (RAID 1 or RAID 5).
Spare drives are assigned to all logical drives in an array automatically and can
be assigned to multiple arrays connected to the same controller.