IBM TOTAL STORAGE DS8000 User Manual
Page 347
availability
The
degree
to
which
a
system
or
resource
is
capable
of
performing
its
normal
function.
See
data
availability.
B
bay
The
physical
space
that
is
used
for
installing
SCSI,
ESCON,
and
fibre-channel
host
adapter
cards.
The
DS8000
has
four
bays,
two
in
each
cluster.
See
also
service
boundary.
bit
1)
Either
of
the
digits
0
or
1
when
used
in
the
binary
numeration
system.
(T)
2)
The
storage
medium
required
to
store
a
single
binary
digit.
See
also
byte.
block
A
string
of
data
elements
recorded
or
transmitted
as
a
unit.
The
elements
may
be
characters,
words,
or
physical
records.
(T)
A
group
of
consecutive
bytes
used
as
the
basic
storage
unit
in
fixed-block
architecture
(FBA).
All
blocks
on
the
storage
device
are
the
same
size
(fixed
size).
See
also
fixed-block
architecture
and
data
record.
byte
1)
A
group
of
eight
adjacent
binary
digits
that
represent
one
EBCDIC
character.
2)
The
storage
medium
required
to
store
eight
bits.
See
also
bit.
C
cache
A
special-purpose
buffer
storage,
smaller
and
faster
than
main
storage,
used
to
hold
a
copy
of
instructions
and
data
obtained
from
main
storage
and
likely
to
be
needed
next
by
the
processor.
(T)
cache
fast
write
A
form
of
the
fast-write
operation
in
which
the
storage
server
writes
the
data
directly
to
cache,
where
it
is
available
for
later
destaging.
cache
hit
An
event
that
occurs
when
a
read
operation
is
sent
to
the
cluster,
and
the
requested
data
is
found
in
cache.
Contrast
with
cache
miss.
cache
memory
Memory,
typically
volatile
memory,
that
a
storage
server
uses
to
improve
access
times
to
instructions
or
data.
The
cache
memory
is
typically
smaller
and
faster
than
the
primary
memory
or
storage
medium.
In
addition
to
residing
in
cache
memory,
the
same
data
also
resides
on
the
storage
devices
in
the
storage
unit.
cache
miss
An
event
that
occurs
when
a
read
operation
is
sent
to
the
cluster,
but
the
data
is
not
found
in
cache.
Contrast
with
cache
hit.
call
home
A
communication
link
established
between
the
DS8000
and
a
service
provider.
The
DS8000
can
use
this
link
to
place
a
call
to
IBM
or
to
another
service
provider
when
it
requires
service.
With
access
to
the
machine,
service
personnel
can
perform
service
tasks,
such
as
viewing
error
logs
and
problem
logs
or
initiating
trace
and
dump
retrievals.
See
also
heartbeat
and
remote
technical
assistance
information
network.
cascading
1)
Connecting
network
controllers
to
each
other
in
a
succession
of
levels
to
concentrate
many
more
lines
than
a
single
level
permits.
2)
In
high-availability
cluster
multiprocessing
(HACMP),
cascading
pertains
to
a
cluster
configuration
in
which
the
cluster
node
with
the
highest
priority
for
a
particular
resource
acquires
the
resource
if
the
primary
node
fails.
The
cluster
node
relinquishes
the
resource
to
the
primary
node
upon
reintegration
of
the
primary
node
into
the
cluster.
catcher
A
server
that
service
personnel
use
to
collect
and
retain
status
data
that
an
DS8000
sends
to
it.
CCR
See
channel
command
retry.
CCW
See
channel
command
word.
CD
See
compact
disc.
CEC
See
computer-electronic
complex.
channel
For
zSeries,
the
part
of
a
channel
subsystem
that
manages
a
single
I/O
interface
between
a
channel
subsystem
and
a
set
of
control
units.
Glossary
327