LSI MegaRAID Express 500 - Manual (Page 137)

Glossary 123
Glossary, Continued
Disk Striping A type of disk array mapping. Consecutive stripes of data are mapped round-robin to
consecutive array members. A striped array (RAID Level 0) provides high I/O
performance at low cost, but provides lowers data reliability than any of its member disks.
Disk Subsystem A collection of disks and the hardware that connects them to one or more host computers.
The hardware can include an intelligent controller or the disks can attach directly to a host
computer I/O a bus adapter.
Double Buffering A technique that achieves maximum data transfer bandwidth by constantly keeping two
I/O requests for adjacent data outstanding. A software component begins a double-
buffered I/O stream by issuing two requests in rapid sequence. Thereafter, each time an
I/O request completes, another is immediately issued. If the disk subsystem is capable of
processing requests fast enough, double buffering allows data to be transferred at the full-
volume transfer rate.
Failed Drive A drive that has ceased to function or consistently functions improperly.
Fast SCSI A variant on the SCSI-2 bus. It uses the same 8-bit bus as the original SCSI-1, but runs at
up to 10 MB (double the speed of SCSI-1.)
Firmware Software stored in read-only memory (ROM) or Programmable ROM (PROM). Firmware
is often responsible for the behavior of a system when it is first turned on. A typical
example would be a monitor program in a computer that loads the full operating system
from disk or from a network and then passes control to the operating system.
FlexRAID Power Fail Option The FlexRAID Power Fail option allows a reconstruction to restart if a
power failure occurs. This is the advantage of this option. The disadvantage is, once the
reconstruction is active, the performance is slower because an additional activity is added.
Cont’d