write
applications
to
source
volumes
and
wait
for
all
pending
updates
to
be
copied
to
the
recovery
site.
At
this
point,
you
can
create
a
FlashCopy
operation
at
your
recovery
site
to
obtain
a
consistent
data.
The
Global
Copy
function
can
operate
at
very
long
distances—well
beyond
the
300
km
distance
that
is
supported
for
Metro
Mirror—and
with
minimal
impact
to
applications,
with
the
distance
that
is
limited
only
by
the
network
and
the
channel
extended
technology.
During
a
disaster,
data
can
be
restored
only
to
the
last
known
consistent
increment
that
was
created.
This
means
that
data
that
is
written
to
the
production
site
but
is
waiting
to
be
transferred
to
the
recovery
site
is
lost
whenever
the
two
storage
units
can
no
longer
communicate.
Be
aware
that
the
use
of
Global
Copy
functions
do
not
guarantee
against
data
loss.
Global
Mirror
functions,
on
the
other
hand,
provide
recoverable
copies
of
production
data
at
a
long
distance
recovery
site
by
continually
forming
consistent
sets
of
data
with
no
significant
performance
impact.
This
allows
a
quick
restart
at
your
recovery
site
in
case
of
a
disaster
at
the
production
site.
The
following
describes
the
Global
Copy
write
sequence:
1.
During
a
Global
Copy
operation,
the
storage
unit
at
your
production
site
captures
information
about
updates
to
the
source
and
periodically
sends
those
updates
to
the
target
volume
at
the
recovery
site.
2.
After
the
initial
copy
of
tracks,
the
storage
unit
series
periodically
starts
a
synchronization
cycle
where
all
updated
tracks,
in
ascending
order
from
the
lowest
numbered
track,
is
copied
from
the
source
volume
to
the
target
volume.
The
storage
unit
updates
the
target
tracks
with
the
current
information
for
that
track,
regardless
of
the
number
of
updates
between
the
time
that
it
was
last
copied,
the
current
time,
and
the
order
in
which
the
updates
occurred.
3.
When
this
process
completes,
the
cycle
is
repeated.
There
is
little
response
time
degradation
on
application
write
operations
in
extended
distance
mode.
4.
Write
updates
to
the
source
volume
receive
an
immediate
completion
because
the
synchronization
cycle
is
independent
of
the
updates
to
the
source
volume.
Global
Mirror
Global
Mirror
provides
a
long-distance
remote
copy
solution
across
two
sites
for
open
systems
or
z/OS
(or
both)
data
using
asynchronous
technology.
Global
Mirror
provides
a
two-site
extended
distance
remote
copy
option
for
disaster
recovery.
With
Global
Mirror,
the
data
that
the
host
writes
to
the
storage
unit
at
the
production
(local)
site
is
asynchronously
shadowed
to
the
storage
unit
at
the
recovery
site.
The
recovery
site
can
be
located
well
beyond
the
300
km
limit
that
is
associated
with
Metro
Mirror
with
minimal
delays
in
response
times.
Separating
volumes
by
larger
distances
provides
greater
protection
against
regional
disasters.
Only
the
capabilities
of
the
network
and
channel
extension
technologies
limit
distance.
Global
Mirror
is
based
on
existing
Copy
Services
functions:
Global
Copy
and
FlashCopy.
With
Global
Mirror,
a
consistent
copy
of
the
data
is
automatically
maintained
on
the
storage
unit
at
the
recovery
site.
This
consistency
is
ensured
if
the
order
of
dependent
write
operations
to
disks
or
disk
groups
is
maintained.
With
Global
Copy
operations,
data
consistency
is
guaranteed
at
the
recovery
site
by
creating
″
freeze
and
run
″
tasks
and
then
using
FlashCopy
to
create
point-in-time
copies
at
the
recovery
site.
118
DS8000
User’s
Guide
Summary of Contents for TotalStorage DS8000
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