
storage
units)
internally
manages
data
consistency
using
consistency
groups
within
a
Global
Mirror
configuration.
Consistency
groups
can
be
created
many
times
per
hour
to
increase
the
currency
of
data
that
is
captured
in
the
consistency
groups
at
the
remote
site.
Note:
A
consistency
group
is
a
collection
of
volumes
(grouped
in
a
session)
across
multiple
storage
units
that
are
managed
together
in
a
session
during
the
creation
of
consistent
copies
of
data.
The
formation
of
these
consistency
groups
is
coordinated
by
the
master
storage
unit,
which
sends
commands
over
remote
mirror
and
copy
links
to
its
subordinate
storage
units.
In
a
two-site
Global
Mirror
configuration,
if
you
have
a
disaster
at
your
local
site
and
have
to
start
production
at
your
remote
site,
you
can
use
the
consistent
point-in-time
data
from
the
consistency
group
at
your
remote
site
to
recover
when
the
local
site
is
operational.
In
a
three-site
Metro/Global
Mirror
configuration,
if
you
have
a
disaster
at
your
local
site
and
you
must
start
production
at
either
your
intermediate
or
remote
site,
you
can
use
the
consistent
point-in-time
data
from
the
consistency
group
at
your
remote
site
to
recover
when
the
local
site
is
operational.
Performing
failover
and
failback
operations
(without
Global
Mirror)
In
the
event
of
a
planned
outage,
such
as
a
scheduled
maintenance
or
an
unplanned
outage,
such
as
a
hardware
failure
that
disables
the
operation
of
your
production
site,
you
can
perform
a
failover
operation
to
your
recovery
site
to
continue
operations.
After
your
production
site
is
operational,
you
can
perform
a
subsequent
failback
operation
to
move
production
back
to
its
original
location.
Moving
production
to
Site
B
after
planned
outages
(failover)
When
you
schedule
a
planned
outage
at
your
production
site
(Site
A),
you
can
switch
production
to
your
recovery
site
(Site
B),
allowing
the
processing
of
data
to
resume
at
Site
B.
This
process
is
known
as
a
failover
recovery.
The
storage
units
at
both
Site
A
and
Site
B
must
be
functional
and
accessible.
In
a
disaster
recovery
environment,
when
two
storage
units
are
set
up
in
two
geographically
distinct
locations,
the
storage
unit
at
the
production
or
local
site
is
referred
to
as
Site
A
and
the
storage
unit
at
the
remote
or
recovery
site
as
Site
B.
For
this
scenario,
assume
that
all
I/O
to
Site
A
has
ceased
because
of
a
planned
outage,
such
as
a
scheduled
maintenance.
The
failover
operation
is
issued
to
the
storage
unit
that
will
become
the
primary.
That
is,
production
is
moved
to
Site
B
during
this
outage,
which
makes
the
target
volumes
at
Site
B
convert
to
source
volumes
and
causes
them
to
enter
a
suspended
state.
Your
original
source
volumes
at
Site
A
remain
in
the
state
they
were
in
at
the
time
of
the
site
switch.
provides
an
example
of
the
implementation
of
failover
and
failback
operations.
Note:
The
failover
recovery
operation
does
not
reverse
the
direction
of
a
remote
mirror
and
copy
pair.
It
changes
a
target
volume
into
a
suspended
source
volume,
while
leaving
the
source
volume
in
its
current
state.
The
following
assumptions
are
made
for
this
scenario:
154
DS8000
User’s
Guide
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