unit
address
For
System
z,
the
address
associated
with
a
device
on
a
given
control
unit.
On
ESCON
interfaces,
the
unit
address
is
the
same
as
the
device
address.
On
OEMI
interfaces,
the
unit
address
specifies
a
control
unit
and
device
pair
on
the
interface.
unprotected
volume
An
AS/400
term
that
indicates
that
the
AS/400
host
recognizes
the
volume
as
an
unprotected
device,
even
though
the
storage
resides
on
a
RAID-formatted
array
and
is,
therefore,
fault
tolerant
by
definition.
The
data
in
an
unprotected
volume
can
be
mirrored.
Also
referred
to
as
an
unprotected
device.
upper-layer
protocol
The
layer
of
the
Internet
Protocol
(IP)
that
supports
one
or
more
logical
protocols
(for
example,
a
SCSI-command
protocol
and
an
ESA/390
command
protocol).
Refer
to
ANSI
X3.230-199x.
UTC
See
Coordinated
Universal
Time.
V
virtual
machine
facility
A
virtual
data
processing
machine
that
appears
to
the
user
to
be
for
the
exclusive
use
of
that
user,
but
whose
functions
are
accomplished
by
sharing
the
resources
of
a
shared
data
processing
system.
An
alternate
name
for
the
VM/370
IBM
operating
system.
vital
product
data
(VPD)
Information
that
uniquely
defines
the
system,
hardware,
software,
and
microcode
elements
of
a
processing
system.
VM
The
root
name
of
several
IBM
operating
systems,
such
as
VM/XA,
VM/ESA
®
,
VM/CMS,
and
z/VM.
See
also
virtual
machine
facility.
volume
For
System
z,
the
information
recorded
on
a
single
unit
of
recording
medium.
Indirectly,
it
can
refer
to
the
unit
of
recording
medium
itself.
On
a
nonremovable-medium
storage
device,
the
term
can
also
indirectly
refer
to
the
storage
device
associated
with
the
volume.
When
multiple
volumes
are
stored
on
a
single
storage
medium
transparently
to
the
program,
the
volumes
can
be
referred
to
as
logical
volumes.
volume
group
A
collection
of
either
physical
or
logical
volumes.
volume
label
A
unique
identifier
that
a
user
assigns
to
a
logical
volume.
VPD
See
vital
product
data.
VSE/ESA
An
IBM
operating
system,
the
letters
of
which
represent
virtual
storage
extended/enterprise
systems
architecture.
W
weight
distribution
area
The
area
that
is
required
to
distribute
the
weight
of
the
storage
unit.
worldwide
node
name
(WWNN)
A
unique
64-bit
identifier
for
a
host
that
contains
a
fibre-channel
port.
See
also
worldwide
port
name.
worldwide
port
name
(WWPN)
A
unique
64-bit
identifier
associated
with
a
fibre-channel
adapter
port.
It
is
assigned
in
an
implementation-
and
protocol-independent
manner.
See
also
worldwide
node
name
write
hit
A
write
operation
in
which
the
requested
data
is
in
the
cache.
write
penalty
The
performance
impact
of
a
classical
RAID-5
write
operation.
WWNN
See
worldwide
node
name.
WWPN
See
worldwide
port
name.
Z
z/Architecture
An
IBM
architecture
for
mainframe
computers
and
peripherals.
The
System
z
family
of
products
uses
the
z/Architecture
architecture.
It
is
the
successor
to
the
S/390
and
9672
family
of
servers.
See
also
System
z.
212
DS8000
User’s
Guide
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