logical
device
The
facilities
of
a
storage
server
(such
as
the
DS8000)
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
zSeries
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
zSeries,
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.
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
can
have
up
to
16
CKD-formatted
logical
subsystems
(4096
CKD
logical
devices)
and
also
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
zSeries
control-unit
image.
For
zSeries
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.
logical
volume
The
storage
medium
that
is
associated
with
a
logical
disk
drive.
A
logical
volume
typically
resides
on
one
or
more
storage
devices.
The
DS8000
administrator
defines
this
unit
of
storage.
The
logical
volume,
when
residing
on
a
RAID-formatted
array,
is
spread
over
the
drives
in
the
array.
logical
volume
manager
(LVM)
A
set
of
system
commands,
library
routines,
and
other
tools
that
allow
the
user
to
establish
and
control
logical
volume
storage.
The
LVM
maps
data
between
the
logical
view
of
storage
space
and
the
physical
disk
drive
module.
longitudinal
redundancy
check
(LRC)
1)
A
method
of
error
checking
during
data
transfer
that
involves
checking
parity
on
a
row
of
binary
digits
that
are
members
of
a
set
that
forms
a
matrix.
Longitudinal
redundancy
check
is
also
called
a
longitudinal
parity
check.
2)
A
mechanism
that
the
DS8000
uses
for
locating
errors.
The
LRC
checks
the
data
as
it
progresses
from
the
host,
through
theDS8000
controller,
into
the
device
adapter,
and
to
the
array.
longwave
laser
adapter
A
connector
that
is
used
between
a
host
and
the
DS8000
to
support
longwave
fibre-channel
communication.
loop
The
physical
connection
between
a
pair
of
device
adapters
in
the
DS8000.
See
also
device
adapter
.
LPAR
See
logical
partition
.
182
DS8000
User’s
Guide
Summary of Contents for TotalStorage DS8000
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