45xx Modular Disk Subsystem Manual for G-Series Releases

45xx Modular Disk Subsystem Manual for G-Series Releases—142466
Glossary-1
Glossary
45xx modular disk subsystem. A disk subsystem consisting of up to eight 2-gigabyte (GB),
4-GB, 8-GB, or 18-GB, 3.5-inch, 45xx disk drives in a module. Two of these modules
(up to 16 disk drives) can be mounted in a frame that is part of the Tandem modular
storage system. Up to 10 modules can be stacked to provide up to 1440 gigabytes of
formatted storage while using only 0.6 square meters (6.3 square feet) of floor space.
Each module communicates with a Tandem system through one or two 6760 ServerNet
adapters.
6760 ServerNet device adapter (SNDA). A ServerNet adapter that controls external disk or
tape drives installed in a modular storage subsystem. The 6760 SNDA contains up to
four ServerNet addressable controllers (SACs), each of which can control one disk
module containing up to 8 disk drives or one tape module containing 2 tape drives.
back-end board (BEB). A component that translates fiber-optic signals from a ServerNet
addressable controller (SAC) into small computer system interface (SCSI) commands
and information for a 45xx disk drive. A 45xx disk module can have one or two back-
end boards (BEBs).
backplane. A board that has connectors on one or both sides of the board, into which circuit
board assemblies plug.
BACKUP utility. A Tandem software utility that creates a backup copy of one or more disk
files on magnetic tape. See also RESTORE utility
.
BEB. See back-end board (BEB)
.
buffer. A block of memory or a storage device that temporarily stores data being transferred
from one device to another. The buffer compensates for the different processing rates of
the devices and their controllers.
central processing unit (CPU). Historically, the main data processing unit of a computer. A
Tandem system has multiple cooperating processors rather than a single CPU. See also
processor
.
controller. See ServerNet addressable controller (SAC)
.
CPU. See central processing unit (CPU).
CRU. See customer-replaceable unit (CRU).
customer-replaceable unit (CRU). A component that can be installed and replaced by
customers without special tools or special Tandem training.
disk drive. A device that stores and accesses data on a disk. There are two types of disk
drives: magnetic and optical. Random access to addressable locations on a magnetic disk
is provided by magnetic read/write heads. Random access to addressable locations on an