HP StorageWorks 2300 - Disk System, User Manual

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Product Description 33
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Definitions
The following terms have specific meanings in the context of this guide:
High availability (HA)
HA describes hardware and software systems that are designed to
minimize planned and unplanned downtime. High availability is
measured at the system level and stated as the percentage of time the
system is in a state to do useful work; for example, 99.95% availability
translates to four hours of downtime per year.
Hot-pluggable
Hot-pluggable signifies the ability of a component to be installed or
replaced without interrupting storage operations and within the
restrictions of the operating environment. All customer-replaceable
disk system components can be replaced under power. Adding or
replacing disks or BCCs may require the use of HP-UX commands to
manage file systems.
JBOD
Pronounced jay-bod, a JBOD (Just a Bunch Of Disks) is an enclosed
group of disks.
LVD
LVD (Low Voltage Differential) is a type of SCSI signalling that filters
out common mode noise by taking the difference of two low-voltage
signals. LVD supports cable lengths up to 25 meters including SCSI
cable lengths inside devices on the bus. The disk system’s connection
to the host is LVD.
PDU and PDRU
PDUs (power distribution units) distribute power from a single inlet to
multiple outlets. PRUs (power relay units) connect one or more PDU
inlets to a single on/off switch, such as a cabinet power switch. Units
that both distribute and switch power are referred to as PDRUs.