Specifications

Technology Overview

Xserve RAID

UPS support

A single Xserve RAID power supply can sustain the system in the event of a power

outage or electrical surge. Each RAID controller has its own DB-9 serial port, allowing

Xserve RAID to connect to and monitor up to two UPS sources. When the system

detects that input power has been switched to a UPS source, it changes the cache

mode from high-performance write-back to safer write-through cache—protecting

data transactions should the UPS fail. If the UPS system is capable of reporting a low

power level, Xserve RAID can alert the administrator of the condition, permitting a

manual shutdown before the power runs out.

Cache Backup Battery Modules

With optional Cache Backup Battery Modules in Xserve RAID, data transactions in the

RAID controller cache are protected for more than 72 hours after an input power failure.

Once power is restored, Xserve RAID writes the transactions and begins recharging the

batteries. If battery power is low, the system remains in write-through cache mode until

the battery charge exceeds 50 percent, when it returns to write-back mode.

Hot sparing

For each RAID controller, any drives not assigned to an array are automatically used

as global hot spares. If a drive fails, the RAID controller rebuilds its data on the spare

drive without requiring intervention by the administrator. The rebuild operation occurs

in the background while the controller processes normal host reads and writes—

so service continues uninterrupted.

To promote the best mix of performance and

rebuild speed, the rebuild rate varies with the amount of trac, or fabric load, on the

RAID controller. As soon as the administrator replaces the failed drive, Xserve RAID

congures it as a new global hot spare for the array.

Easy serviceability

Power supplies, cooling modules, RAID controller modules, and hard drives can be

removed and replaced in seconds without tools. These components are all hot-

swappable, with the exception of the RAID controllers, which are warm-swappable,

meaning they can be replaced without interrupting data availability. In addition, Xserve

RAID has a shutdown feature that allows for planned maintenance without running

down the cache backup batteries. This feature can also be benecial if Xserve RAID is

stored for long periods of time.