IBM TOTAL STORAGE DS8000 User Manual
Page 351
data
field
The
optional
third
field
of
a
count
key
data
(CKD)
record.
The
count
field
specifies
the
length
of
the
data
field.
The
data
field
contains
data
that
the
program
writes.
data
record
The
basic
unit
of
zSeries
storage
on
a
DS8000,
also
known
as
a
count-key-data
(CKD)
record.
Data
records
are
stored
on
a
track.
The
records
are
sequentially
numbered
starting
with
0.
The
first
record,
R0,
is
typically
called
the
track
descriptor
record
and
contains
data
that
the
operating
system
normally
uses
to
manage
the
track.
See
also
count-key-data
and
fixed-block
architecture.
data
set
FlashCopy
For
zSeries
hosts,
a
feature
of
FlashCopy
that
indicates
how
many
partial
volume
FlashCopy
relationships
are
active
on
a
volume.
data
sharing
The
ability
of
multiple
host
systems
to
concurrently
utilize
data
that
they
store
on
one
or
more
storage
devices.
The
storage
unit
enables
configured
storage
to
be
accessible
to
any,
or
all,
attached
host
systems.
To
use
this
capability,
the
host
program
must
be
designed
to
support
data
that
it
is
sharing.
DDM
See
disk
drive
module.
DDM
group
See
disk
pack.
dedicated
storage
Storage
within
a
storage
unit
that
is
configured
such
that
a
single
host
system
has
exclusive
access
to
the
storage.
demote
To
remove
a
logical
data
unit
from
cache
memory.
A
storage
server
demotes
a
data
unit
to
make
room
for
other
logical
data
units
in
the
cache
or
because
the
logical
data
unit
is
not
valid.
The
storage
unit
must
destage
logical
data
units
with
active
write
units
before
they
can
be
demoted.
See
also
destage.
destage
To
move
data
from
an
online
or
higher
priority
to
an
offline
or
lower
priority
device.
The
storage
unit
stages
incoming
data
into
cache
and
then
destages
it
to
disk.
device
For
zSeries,
a
disk
drive.
device
adapter
(DA)
A
physical
component
of
the
DS8000
that
provides
communication
between
the
clusters
and
the
storage
devices.
The
DS8000
has
eight
device
adapters
that
it
deploys
in
pairs,
one
from
each
cluster.
Device
adapter
pairing
enables
the
DS8000
to
access
any
disk
drive
from
either
of
two
paths,
providing
fault
tolerance
and
enhanced
availability.
device
address
For
zSeries,
the
field
of
an
ESCON
device-level
frame
that
selects
a
specific
device
on
a
control-unit
image.
device
ID
The
unique
two-digit
hexadecimal
number
that
identifies
the
logical
device.
device
interface
card
A
physical
subunit
of
a
storage
cluster
that
provides
the
communication
with
the
attached
device
drive
modules.
device
number
For
zSeries,
a
four-hexadecimal-character
identifier,
for
example
13A0,
that
the
systems
administrator
associates
with
a
device
to
facilitate
communication
between
the
program
and
the
host
operator.
The
device
number
is
associated
with
a
subchannel.
device
sparing
A
subsystem
function
that
automatically
copies
data
from
a
failing
device
drive
module
to
a
spare
device
drive
module.
The
subsystem
maintains
data
access
during
the
process.
DFS
See
distributed
file
service.
DFSMS
See
Data
Facility
Storage
Management
Subsystem.
direct
access
storage
device
(DASD)
1)
A
mass
storage
medium
on
which
a
computer
stores
data.
2)
A
disk
device.
Glossary
331