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With
Global
Mirror,
the
data
that
the
host
writes
to
the
storage
unit
at
the
local
site
is
asynchronously
shadowed
to
the
storage
unit
at
the
remote
site.
A
consistent
copy
of
the
data
is
then
automatically
maintained
on
the
storage
unit
at
the
remote
site.
Use
of
Global
Mirror
does
not
guarantee
against
data
loss.
During
a
disaster,
data
can
only
be
restored
to
the
last
known
consistent
increment
that
was
created.
This
means
that
data
that
is
written
to
the
primary
site
and
is
waiting
to
be
transferred
to
the
secondary
site
is
lost
whenever
the
two
storage
units
can
no
longer
communicate.
The
following
considerations
apply
when
you
use
the
Global
Mirror
recovery
process:
v
The
Global
Mirror
master
might
still
be
running
at
the
local
site,
especially
if
the
disaster
at
the
local
site
is
a
rolling
disaster
in
which
not
all
components
fail
simultaneously.
v
The
consistent
copy
at
the
remote
site
is
not
the
secondary
volume,
but
it
is
the
FlashCopy
target
whose
source
is
the
secondary
volume.
v
Formation
of
a
consistency
group
might
have
been
in
progress
at
the
time
of
the
failure.
v
You
can
speed
up
recovery
processing
by
choosing
the
Fast
Reverse
restore
process
that
is
explained
later
in
this
section.
Perform
the
following
steps
to
use
Global
Mirror
for
an
unplanned
failover
using
the
DS
Storage
Manager.
You
can
also
use
the
DS
CLI
for
these
steps.
Note:
For
details
on
individuals
tasks,
see
the
related
topics
section.
1.
Enter
the
Global
Mirror
session
at
the
local
site.
Note:
Wait
until
the
master
storage
unit
completes
the
termination
processing
or
enters
the
fatal
state
before
continuing
with
the
next
step.
Of
course,
this
might
not
be
possible
if
the
local
site
has
completely
failed.
If
that
is
the
case,
proceed
to
the
next
step
without
waiting.
2.
Issue
a
recovery
failover
request
on
the
Global
Copy
volumes
pair
to
force
a
stop
of
the
Volume
A
to
Volume
B
extended
distance
relationship
and
create
a
Volume
B
to
Volume
A
Global
Copy
relationship.
Note:
All
B
volumes
must
successfully
process
the
recovery
failover
request
before
you
can
move
to
the
next
step.
3.
Look
at
the
session
properties
for
Volume
B
and
Volume
C
to
ascertain
the
state
of
the
consistency
group
between
the
B
volume
and
C
volume.
You
are
looking
primarily
at
the
FlashCopy
relationships
and
your
analysis
determines
your
next
step
in
the
recovery
process.
Act
on
your
analysis
as
follows:
a.
FlashCopy
relationships
are
nonrestorable
and
all
the
sequence
numbers
are
equal.
No
action
to
the
consistency
group
is
necessary.
b.
FlashCopy
relationships
are
restorable
and
all
the
sequence
numbers
are
equal.
Issue
the
FlashCopy
Discard
changes
command
to
all
the
FlashCopy
relationships
in
the
consistency
group.
c.
All
the
FlashCopy
sequence
numbers
are
equal
and
at
least
one
of
the
FlashCopy
relationships
is
nonrestorable.
Issue
a
FlashCopy
Commit
changes
command
to
all
the
FlashCopy
relationships
in
the
consistency
group
that
are
restorable.
150
DS8000
User’s
Guide
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