Compaq Smart Array 221 User Manual page 111

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 do 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 four online spares for each Smart Array 221 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).
Writer: Karen Hale Project: Compaq Smart Array 221 Controller User Guide Comments: 388541-001
File Name: K-APPC.DOC Last Saved On: 11/5/98 1:40 PM
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Compaq Smart Array 221 Controller User Guide
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