IBM TOTAL STORAGE DS8000 User Manual
Page 350
Copy
Services
server
A
cluster
that
the
Copy
Services
administrator
designates
to
perform
the
DS8000
Copy
Services
functions.
Copy
Services
server
group
A
collection
of
user-designated
DS8000
clusters
participating
in
Copy
Services
functions
that
a
designated,
active,
Copy
Services
server
manages.
A
Copy
Services
server
group
is
also
called
a
Copy
Services
domain.
count
field
The
first
field
of
a
count
key
data
(CKD)
record.
This
eight-byte
field
contains
a
four-byte
track
address
(CCHH).
It
defines
the
cylinder
and
head
that
are
associated
with
the
track,
and
a
one-byte
record
number
(R)
that
identifies
the
record
on
the
track.
It
defines
a
one-byte
key
length
that
specifies
the
length
of
the
record’s
key
field
(0
means
no
key
field).
It
defines
a
two-byte
data
length
that
specifies
the
length
of
the
record’s
data
field
(0
means
no
data
field).
Only
the
end-of-file
record
has
a
data
length
of
zero.
count
key
data
(CKD)
For
zSeries,
a
data-record
format
employing
self-defining
record
formats
in
which
each
record
is
represented
by
up
to
three
fields:
a
count
field
that
identifies
the
record
and
specifies
its
format,
an
optional
key
field
that
identifies
the
data
area
contents,
and
an
optional
data
field
that
typically
contains
the
user
data.
For
CKD
records
on
the
storage
unit,
the
logical
volume
size
is
defined
in
terms
of
the
device
emulation
mode
(3390
or
3380
track
format).
The
count
field
is
always
8
bytes
long
and
contains
the
lengths
of
the
key
and
data
fields,
the
key
field
has
a
length
of
0
to
255
bytes,
and
the
data
field
has
a
length
of
0
to
65
535
or
the
maximum
that
will
fit
on
the
track.
See
also
data
record.
CPC
See
cluster
processor
complex.
CRC
See
cyclic
redundancy
check.
CU
See
control
unit.
CUIR
See
control-unit
initiated
reconfiguration.
custom
volume
A
volume
in
count-key-data
(CKD)
format
that
is
not
a
standard
volume,
which
means
that
it
does
not
necessarily
present
the
same
number
of
cylinders
and
capacity
to
its
assigned
logical
control
unit
as
provided
by
one
of
the
following
standard
zSeries
volume
types:
3390-2,
3390-3,
3390-9,
3390-2
(3380-track
mode),
or
3390-3
(3380-track
mode).
See
also
count-key-data,
interleave,
standard
volume,
and
volume.
CUT
See
Coordinated
Universal
Time.
cyclic
redundancy
check
(CRC)
A
redundancy
check
in
which
the
check
key
is
generated
by
a
cyclic
algorithm.
(T)
cylinder
A
unit
of
storage
on
a
CKD
device
with
a
fixed
number
of
tracks.
D
DA
See
device
adapter.
See
also
IBM
Serial
Storage
adapter.
daisy
chain
See
serial
connection.
DASD
See
direct
access
storage
device.
DASD
fast
write
(DFW)
A
function
of
a
storage
server
in
which
active
write
data
is
stored
in
nonvolatile
cache,
thus
avoiding
exposure
to
data
loss.
data
availability
The
degree
to
which
data
is
available
when
needed,
typically
measured
as
a
percentage
of
time
that
the
system
would
be
capable
of
responding
to
any
data
request
(for
example,
99.999%
available).
data
compression
A
technique
or
algorithm
used
to
encode
data
such
that
the
encoded
result
can
be
stored
in
less
space
than
the
original
data.
The
original
data
can
be
recovered
from
the
encoded
result
through
a
reverse
technique
or
reverse
algorithm.
See
also
compression.
Data
Facility
Storage
Management
Subsystem
(DFSMS)
An
operating
environment
that
helps
automate
and
centralize
the
management
of
storage.
To
manage
storage,
DFSMS
provides
the
storage
administrator
with
control
over
data
class,
storage
class,
management
class,
storage
group,
and
automatic
class
selection
routine
definitions.
330
IBM
TotalStorage
DS8000:
Messages
Reference