link-level
facility
The
ESCON
hardware
and
logical
functions
of
a
control
unit
or
channel
subsystem
that
allow
communication
over
an
ESCON
write
interface
and
an
ESCON
read
interface.
local
area
network
(LAN)
A
computer
network
located
on
a
user’s
premises
within
a
limited
geographic
area.
local
An
configuration
option
for
storage
servers
that
are
connected
to
a
host-system
network
that
does
not
have
a
domain
name
system
(DNS)
server.
logical
address
On
an
ESCON
interface,
the
portion
of
a
source
or
destination
address
in
a
frame
used
to
select
a
specific
channel-subsystem
or
control-unit
image.
logical
block
address
(LBA)
The
address
assigned
by
the
DS8000
to
a
sector
of
a
disk.
logical
control
unit
(LCU)
See
control-unit
image.
logical
data
unit
A
unit
of
storage
that
is
accessible
on
a
given
device.
logical
device
The
facilities
of
a
storage
server
(such
as
the
DS8000
series)
associated
with
the
processing
of
I/O
operations
directed
to
a
single
host-accessible
emulated
I/O
device.
The
associated
storage
is
referred
to
as
a
logical
volume.
The
logical
device
is
mapped
to
one
or
more
host-addressable
units,
such
as
a
device
on
a
System
z
I/O
interface
or
a
logical
unit
on
a
SCSI
I/O
interface,
such
that
the
host
initiating
I/O
operations
to
the
I/O-addressable
unit
interacts
with
the
storage
on
the
associated
logical
device.
logical
partition
(LPAR)
For
System
z,
a
set
of
functions
that
create
the
programming
environment
in
which
more
than
one
logical
partition
(LPAR)
is
established
on
a
processor.
An
LPAR
is
conceptually
similar
to
a
virtual
machine
environment
except
that
the
LPAR
is
a
function
of
the
processor.
Also,
the
LPAR
does
not
depend
on
an
operating
system
to
create
the
virtual
machine
environment.
(DS8000
series
only)
logical
path
1)
The
relationship
between
a
channel
image
and
a
control-unit
image
that
designates
the
physical
path
to
be
used
for
device-level
communications
between
these
images.
The
logical
path
is
established
as
part
of
the
channel
and
control-unit
initialization
procedures
by
the
exchange
of
link-level
frames.
2)
With
the
Remote
Mirror
and
Copy
feature,
the
relationship
between
a
source
logical
subsystem
(LSS)
and
a
target
LSS
that
is
created
over
a
physical
path
through
the
interconnection
fabric
that
is
used
for
Remote
Mirror
and
Copy
functions.
An
LSS
is
a
primary
control
unit,
which
performs
the
functions
of
a
channel
image.
logical
subsystem
(LSS)
A
topological
construct
that
consists
of
a
group
of
up
to
256
logical
devices.
A
DS8000
storage
unit
can
have
(if
CDK
only)
up
to
32
CKD-formatted
logical
subsystems
(8192
CKD
logical
devices)
or
(if
FBA
only)
up
to
32
fixed-block
logical
subsystems
(8192
fixed-block
logical
devices).
If
mixed
CKD
and
FBA,
a
DS8000
can
have
up
to
16
CKD-formatted
logical
subsystems
(4096
CKD
logical
devices)
and
up
to
16
fixed-block
logical
subsystems
(4096
fixed-block
logical
devices).
The
logical
subsystem
facilitates
configuration
of
the
DS8000
and
might
have
other
implications
relative
to
the
operation
of
certain
functions.
There
is
a
one-to-one
mapping
between
a
CKD
logical
subsystem
and
a
System
z
control-unit
image.
For
System
z
hosts,
a
logical
subsystem
represents
a
logical
control
unit
(LCU).
Each
control-unit
image
is
associated
with
only
one
logical
subsystem.
See
also
control-unit
image.
logical
unit
In
open
systems,
a
logical
disk
drive.
logical
unit
number
(LUN)
In
the
SCSI
protocol,
a
unique
number
that
is
used
on
a
SCSI
bus
to
enable
it
to
differentiate
between
separate
devices,
each
of
which
is
a
logical
unit.
200
DS8000
User’s
Guide
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