Redundancy

The provision of multiple interchangeable components to perform a

 

single function to cope with failures or errors. Redundancy normally

 

applies to hardware; disk mirroring is a common form of hardware

 

redundancy.

Replacement

A disk available to replace a failed member disk in a RAID array.

Disk

 

Replacement

A component or collection of components in a disk subsystem that is

Unit

always replaced as a unit when any part of the collection fails. Typical

 

replacement units in a disk subsystem includes disks, controller logic

 

boards, power supplies, and cables. Also called a hot spare.

SAF-TE

SCSI-accessed fault-tolerant enclosure. An industry protocol for

 

managing RAID enclosures and reporting enclosure environmental

 

information.

SCSI

(Small computer system interface) A processor-independent standard for

 

system-level interfacing between a computer and intelligent devices,

 

including hard disks, floppy disks, CD-ROM, printers, scanners, etc.

 

Multiple SCSI devices can be connected to a single host adapter on the

 

computer's bus. SCSI transfers eight or 16 bits in parallel and can

 

operate in either asynchronous or synchronous modes. The synchronous

 

transfer rate is up to 320 Mbytes/s (for Ultra320 SCSI). SCSI connections

 

normally use single-ended drivers, as opposed to differential drivers.

SCSI Channel

MegaRAID controls the disk drives through SCSI-2 buses (channels)

 

over which the system transfers data in either Fast and Wide or Ultra

 

SCSI mode. Each adapter can control up to three SCSI channels.

 

Internal and external disk drives can be mixed on channels 0 and 1, but

 

not on channel 2.

SCSI Drive State A SCSI physical drive can be in one of these states:

•Online: Powered-on and operational.

•Ready: Functioning normally, but not part of a configured logical drive and not designated as a hot spare.

•Hot Spare: Powered-on stand-by disk drive, ready for use if an online disk fails.

•Fail: Out of service, due to a fault occurring on the drive.

•Rebuild: Currently being rebuilt with data from a failed drive.

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Copyright © 2002 by LSI Logic Corporation. All rights reserved.