HD CoD
See High Density Capacity on Demand.
HD frame
See High density frame.
HD slot
See High density slot.
HD2 frame
See High density frame.
head See drive head.
heat output
The amount of heat (in kBtu/hr) that the
TS4500 tape library dissipates during
normal operation.
hertz (Hz)
A unit of frequency equal to cycle per
second.
heterogeneous
Of unlike kind.
hex, hexadecimal
(1) Pertaining to a selection, choice, or
condition that has 16 possible different
values or states.
(2) Pertaining to a fixed-radix numeration
system, with radix of 16.
(3) Pertaining to a system of numbers to
the base 16; hexadecimal digits range
from 0 through 9 and A through F, where
A represents 10 and F represents 15.
high availability (HA)
A product that contains redundancy to
continue work in the case of a set of (but
not all possible) failures. A library that is
HA contains two separate cartridge
accessors.
High Availability Clustered Multiprocessing
(HACMP)
An IBM AIX solution that automatically
detects system or network failures and
eliminates a single point of failure by
managing failover to a recovery processor.
High availability clustering refers to the
linking of two or more computers, one of
which can provide operation if the other
one fails.
High density frame
An expansion frame that contains HD
slots. An HD2 frame is a
second-generation HD frame that can be
installed in the leftmost position (frame 1)
of the library and can be utilized as an
integrated service bay. All expansion
frames that are installed to the left of the
TS4500 base frame, or that are serving as
a TS4500 service bay, must be HD2
frames. Drive-capable HD2 frames
support up to 16 HD2-compatible tape
drives when positioned as frame number
2 or higher. Models L25, L55, D25, D55,
S25, and S55 are all HD2 frames.
Non-HD2 frames cannot be upgraded to
HD2 frames.
High density slot
A four-deep or five-deep container for
cartridges in an HD frame.
High Voltage Differential (HVD)
A logic signaling system that enables data
communication between a supported
server and the TS3500 tape library. HVD
signaling uses a paired plus and minus
signal level to reduce the effects of noise
on the SCSI bus. Any noise that is injected
into the signal is present in both a plus
and minus state, and is thereby canceled.
Synonymous with differential.
homogeneous
Of the same kind.
host The controlling or highest-level system in
a data communication configuration.
Synonymous with server.
host bus adapter (HBA)
An adapter that provides I/O processing
and physical connectivity between a
server and storage.
host cleaning
A method that enables the host (server) to
detect the need to clean a tape drive and
to control the cleaning process. Host
cleaning with a cleaning cartridge is only
supported when automatic cleaning is
disabled, and only for the logical library
in which each cleaning cartridge is stored.
HTTP See Hyper Text Transfer Protocol.
hub A communications device to which nodes
on a multi-point bus or loop are
physically connected. Hubs are commonly
used in Fibre Channel networks to
improve the manageability of physical
cables. They maintain the logical loop
topology of the network of which they are
a part, while they create a “hub and
spoke” physical star layout. Unlike
176 IBM TS4500: Introduction and Planning Guide
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