Apple Xserve RAID Especificaciones descargar pdf (Pagina 15)

Technology Overview

Xserve RAID

Apple Drive Modules

Xserve RAID uses reliable, high-

performance Apple Drive Modules

with true hot-swapping capabilities.

Drive Technology and Capacity

Instead of relying on expensive SCSI or Fibre Channel hard drives, Apple developed

a high-throughput ATA to Fibre Channel storage architecture that delivers superior

performance and reliability at a much lower cost. Xserve RAID achieves its massive

10.5TB capacity with 14 hot-swappable 750GB Apple Drive Modules. The 24/7

enterprise-class rated, high-capacity 7200-rpm Ultra ATA drive modules provide

aordable expansion, maximum reliability, and conguration exibility as storage

needs grow.

Fourteen independent drive channels

The multithreaded Xserve RAID architecture features a dedicated Ultra ATA channel

for each of its 14 drive bays. Drive independence prevents data bottlenecks and

maximizes throughput while enhancing availability. Because each hard drive is isolated

on its own bus, a drive failure doesn’t degrade the accessibility or performance of the

surviving drives. In addition, independent drive channels reduce the complexity and

cost of high-availability storage, since loop redundancy circuits and signal ampliers

aren’t required, as they are in multidrive Fibre Channel and SCSI implementations.

Apple Drive Modules

Hot-plug Apple Drive Modules feature a unique handle design for fast, easy installa-

tion and a positive locking mechanism to hold them tightly in place after insertion.

Sophisticated connectors called SCA II, or Single Connector Attachment II, prevent the

connecting pins from bending when a drive is inserted or removed. Carefully tested

and qualied to ensure maximum performance and reliability, Apple Drive Modules

work seamlessly with RAID Admin, Apple’s innovative remote management and

monitoring software for Xserve RAID.

On-drive cache

Each Apple Drive Module is equipped with up to 16MB of disk cache to accelerate

read and write operations in performance-sensitive applications such as video

editing. On-drive read cache, commonly called “read-ahead” cache, allows the

drive controller to retrieve a block of data before it is required by the host system.

The RAID controller provides instructions to each drive in an array, indicating what

data block is required next and allowing the individual drive controllers to queue

up the data for instant availability.

Similarly, on-drive cache can serve as a holding tank for write data. When this option

is enabled, the RAID controller distributes data to each drive and stores it in cache—

allowing the drive controller to notify the RAID processor immediately that trans-

mission was successful (also known as a “committed write”). This frees up the storage

pipeline for other needs while the data is being written to the drive platters at

maximum speed.

Using on-drive write cache is inherently risky: In the event of a power failure, the

cached data could be lost. For this reason, it is turned o by default in protected

RAID congurations.

Hot-swapping capabilities

The hardware RAID controllers and Apple-designed drive carriers enable true hot-

swapping of Apple Drive Modules. This means a failed drive can be removed and

replaced without interruption in service or loss of data. The system continues to

operate while the contents of the failed drive are rebuilt on a replacement drive

using redundant or parity information. (This feature is not applicable to a RAID 0

or enhanced JBOD conguration, since they do not oer data protection.)

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