
For
this
scenario,
assume
that
Site
A
is
operational
and
that
connectivity
from
Site
B
to
Site
A
is
available.
Use
this
procedure
to
restart
your
production
environment
using
the
volumes
from
Site
B.
After
the
failover
operation
processes,
the
volumes
at
Site
B
are
available
to
be
mounted
and
used
by
a
host.
You
can
use
the
volumes
from
Site
B
to
restart
your
application.
The
failback
operation
resynchronizes
the
volumes
in
the
following
manner
depending
on
the
volume
state:
v
If
a
volume
at
Site
A
is
in
a
simplex
state,
all
of
the
data
for
that
volume
is
sent
from
Site
B
to
Site
A.
v
If
a
volume
at
Site
A
is
in
a
full-duplex
or
suspended
state
and
without
changed
tracks,
only
the
modified
data
on
the
volume
at
Site
B
is
sent
to
the
volume
at
Site
A.
v
If
a
volume
at
Site
A
is
in
a
suspended
state
but
has
tracks
that
have
been
modified,
the
volume
at
Site
B
discovers
which
tracks
were
modified
at
any
site
and
sends
both
the
tracks
that
were
changed
on
Site
A
and
the
tracks
that
were
marked
at
Site
B
from
Site
A
to
Site
B.
The
following
assumptions
are
made
for
this
scenario:
v
Paths
from
Site
B
to
Site
A
are
created.
v
Remote
mirror
and
copy
volume
pairs
are
created.
The
Site
B
volume
is
the
source
volume
of
the
failback
operation.
This
volume
was
initially
the
target
volume
of
the
relationship.
The
following
steps
summarize
the
actions
that
you
must
take
to
return
production
to
your
local
site
after
initiating
a
planned
outage.
1.
Perform
a
failback
operation
at
Site
B.
As
a
result,
data
that
has
been
modified
at
Site
B
for
the
specified
volumes
is
sent
from
Site
B
to
Site
A.
Data
that
was
modified
at
Site
A
after
the
switch
to
Site
B
is
overwritten
by
the
data
from
Site
B.
2.
Quiesce
your
application
(still
updating
volumes
at
Site
B)
to
cease
all
write
I/O
from
updating
the
source
volumes
before
the
application
returns
to
normal
operations.
Depending
on
the
host
operating
system,
it
might
be
necessary
to
unmount
the
source
volumes.
3.
Perform
another
failover
recovery
operation
at
Site
A.
This
process
converts
the
full-duplex
target
volumes
at
Site
A
to
suspended
source
volumes.
The
volumes
at
Site
A
start
the
change
recording
process
while
in
failover
mode.
4.
Rescan
(depending
on
your
operating
system)
the
fibre-channel
devices
and
mount
the
new
source
volumes
at
Site
A.
5.
Restart
the
applications
in
normal
production
at
Site
A
and
check
for
consistency
after
the
failover
operation
completes.
When
your
applications
are
started,
all
write
I/O
to
the
new
source
volumes
are
tracked
by
the
bitmap
that
is
created.
6.
From
Site
A,
create
paths
in
the
opposite
direction
from
Site
A
to
Site
B.
7.
From
Site
A,
perform
another
failover
and
failback
operation
using
the
source
volumes.
This
process
resynchronizes
the
volumes
between
your
Sites
A
and
B.
Start
your
applications
at
Site
A
and
check
for
consistency.
8.
Mount
your
volumes
at
Site
A
and
start
your
applications
on
your
primary
server.
Chapter
10.
Disaster
recovery
using
Copy
Services
157
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