Glossary, Continued

Reconstruct The act of remaking a logical drive after changing RAID levels or adding a physical drive to an existing array.

Redundancy The provision of multiple interchangeable components to perform a single function to cope with failures or errors. Redundancy normally applies to hardware; a common form of hardware redundancy is disk mirroring.

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

Replacement Unit A component or collection of components in a disk subsystem that are 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. SCSI can connect up to 7 devices to a single adapter (or

 

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 40 MB/s. SCSI connections normally use single ended drivers, as opposed to

 

differential drivers. The original standard is now called SCSI-1 to distinguish it from

 

SCSI-2 and SCSI-3, which include specifications of Wide SCSI (a 16-bit bus) and Fast

 

SCSI (10 MB/s transfer).

SCSI Channel

MegaRAID controls the disk drives via 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.

 

Cont’d

128MegaRAID Express 500 Hardware Guide