System information

Working With RAID Arrays 17
5
Choose the options you want.
m “Use RAID Now background initialization” lets you use the RAID array without waiting for
initialization to finish. While the array is being initialized, data read and write speeds will
be somewhat reduced. If this option is off, initialization takes place before the array is
visible on the host system.
Note: The array cannot be seen by the host computer before initialization is complete
unless RAID Now is used.
m “Use drive cache” enables the built-in write cache on each drive in the array. This option
improves efficiency and speed of data transfer, but the drive cache contents will be lost if
power to the system fails, unless you are using an uninterruptible power supply (UPS).
In the event of a power failure, the system detects UPS power and immediately flushes
the data in the drive cache on a drive and then turns off the cache. When AC power is
restored, the system turns on the drive cache again.
6
Check the summary of the array you’ve chosen and click Create Array.
Note: The RAID controller automatically treats any drive not assigned to an array as a global
hot spare for arrays on that controller.
About Spare Drives
A spare drive is any drive that has not been assigned to an array. On the Xserve RAID, an
unassigned drive is “hot” (always spinning and ready for use) and global (available to any
array on its controller). A spare drive is used automatically by the RAID controller for its
group of drives (either drives 1 to 7 or drives 8 to 14) whenever a drive within an array fails.
(A controller can only use available drives on its side of the system; it cannot treat a drive on
the other side as a hot spare.)
When you assign a previously unused drive to a new array, it no longer serves as a hot spare.
Modifying a RAID Array
Once a RAID array is established, you cannot change its type or add and remove drives from
it. You can turn the drive cache on or off.
To modify a RAID array, you must back up all data in the array, delete the array, and create a
new array with the parameters you want.
Important
It is recommended that you use a UPS when you have drive cache enabled.
Without UPS backup, you could lose data in the event of a power failure.