Intergraph InterRAID-8e Hardware User's Manual page 160

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disk array
A collection of disks from one or more disk subsystems combined with array
management software. It controls the disks and presents them to the array
operating environment as one or more virtual disks.
disk mirroring
One disk drive serving as the mirror image of another disk drive. When data is
written to one drive, it is also written to the other. Both drives, therefore, contain
exactly the same information and either drive can provide user data if the other
drive fails.
disk spanning
Several disk drives appearing as one large disk drive. This virtual disk drive can
then store data across the disk drives without the user being concerned about which
drive contains what data.
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 lower data reliability than any of its member
disks.
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.
dual-bus
A SCSI cable configuration of two busses with a dual-bus module installed to link
all drives in the cabinet to two separate channels.
duplexing
The use of two controllers to drive a disk drive subsystem. If a controller fails, the
other is available to provide disk I/O. And, depending on how the controller
software is written, both controllers may work together to read and write data
simultaneously to different drives.
Dynamic Random Access Memory (DRAM)
A memory device architecture providing large amounts of memory storage using
Single Inline Memory Modules (SIMMs). After powering on the system, the
majority of data needed to operate is retrieved from the disk drives and stored in
DRAM. DRAM loses its contents when powered down.