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Table
2.
Comparison
of
licensed
functions
(continued)
Licensed
function
Description
Advantages
Considerations
z/OS
Global
Mirror
Asynchronous
copy
controlled
by
z/OS
host
software
Nearly
unlimited
distance,
highly
scalable,
and
very
low
RPO.
Additional
host
server
hardware
and
software
is
required.
The
RPO
might
grow
if
bandwidth
capability
is
exceeded
or
host
performance
might
be
impacted.
Parallel
Access
Volumes
The
use
of
parallel
access
volumes
(PAVs)
enables
a
single
zSeries
server
to
simultaneously
process
multiple
I/O
operations
to
the
same
logical
volume,
which
can
help
to
significantly
reduce
device
queue
delays.
This
is
achieved
by
defining
multiple
addresses
per
volume.
With
dynamic
parallel
access
volumes,
the
assignment
of
addresses
to
volumes
is
automatically
managed
to
help
the
workload
meet
its
performance
objectives
and
minimize
overall
queuing.
You
must
configure
both
your
storage
unit
and
operating
system
to
use
PAVs.
You
can
use
the
logical
configuration
definition
to
define
PAV-bases,
PAV-aliases,
and
their
relationship
in
the
storage
unit
hardware.
This
unit
address
relationship
creates
a
single
logical
volume,
allowing
concurrent
I/O
operations.
The
storage
unit
supports
concurrent
or
parallel
data
transfer
operations
to
or
from
the
same
volume
from
the
same
system
or
system
image
for
S/390
or
zSeries
hosts.
An
S/390
with
PAV
software
support
enables
multiple
users
and
jobs
to
simultaneously
access
a
logical
volume.
Read
and
write
operations
can
be
accessed
simultaneously
to
different
domains.
(The
domain
of
an
I/O
operation
is
the
specified
extents
to
which
the
I/O
operation
applies.)
DS8000
limitations
The
following
list
describes
known
limitations
for
the
DS8000.
v
The
65,520
cylinder
3390
volume
is
not
supported
with
z/OS
Global
Mirror
and
z/OS
Metro/Global
Mirror.
v
The
amount
of
physical
capacity
within
a
2107
system
that
can
be
logically
configured
for
use
will
be
enforced
by
the
2107
licensed
machine
code
(LMC)
to
maintain
compliance
with
the
extent
of
IBM
authorization
established
for
licensed
functions
activated
on
the
machine.
The
2107
LMC
will
not
allow
the
logical
configuration
of
physical
capacity
beyond
the
extent
of
IBM
authorization
(except
when
activating
Standby
CoD
capacity).
v
The
deactivation
of
an
activated
licensed
function,
or
a
lateral
change
or
reduction
in
the
license
scope,
is
a
disruptive
activity
and
requires
a
machine
IML
(Model
921
and
Model
922)
or
reboot
of
the
affected
image
(Model
9A2).
A
lateral
change
is
defined
as
changing
the
license
scope
from
fixed
block
(FB)
to
count
key
data
(CKD)
or
from
CKD
to
FB.
A
reduction
is
defined
as
changing
the
license
scope
from
all
physical
capacity
(ALL)
to
only
FB
or
only
CKD
capacity.
v
The
following
activities
are
disruptive:
Chapter
1.
Introduction
to
IBM
TotalStorage
DS8000
series
21
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