
For
Global
Mirror
processing,
one
storage
unit
at
the
intermediate
site
is
designated
as
the
master
storage
unit.
The
master
storage
unit
sends
commands
over
Fibre
Channel
Protocol
(FCP)
links
and
coordinates
the
consistency
group
formation
process.
These
links
are
required
for
the
Global
Mirror
master
storage
unit
to
coordinate
the
consistency
group
formation
process
with
the
storage
units
and
to
communicate
the
FlashCopy
commands
to
the
remote
site.
All
status
is
relayed
back
to
the
master
storage
unit.
How
Metro/Global
Mirror
works
In
order
to
understand
how
Metro/Global
Mirror
works,
it
is
important
to
understand
how
the
volumes
are
configured
at
each
site.
shows
a
Metro/Global
Mirror
environment
that
includes
the
A,
B,
C,
and
D
volume
configuration
at
the
three
sites.
There
are
three
volume
configurations
in
a
Metro/Global
Mirror
environment:
v
Volumes
at
the
local
(or
primary)
site
are
Metro
Mirror
primary
(or
source)
volumes
and
are
referred
to
as
the
A
volumes.
v
Volumes
at
the
intermediate
site
are
the
Metro
Mirror
secondary
(or
target)
volumes
and
Global
Mirror
primary
volumes
at
the
same
time.
These
volumes
are
referred
to
as
the
B
volumes.
(If
additional
volumes
are
used
at
the
intermediate
site
as
FlashCopy
target
volumes,
they
are
referred
to
as
E
volumes.)
v
One
set
of
volumes
at
the
remote
site
are
the
Global
Mirror
secondary
volumes
and
FlashCopy
source
volumes
at
the
same
time.
These
volumes
are
referred
to
as
the
C
volumes.
The
FlashCopy
target
volumes
are
referred
to
as
the
D
volumes.
The
Global
Mirror
function
allows
you
to
combine
a
Global
Copy
volume
pair
with
FlashCopy
such
that
the
Global
Copy
secondary
also
serves
as
the
FlashCopy
source
in
a
Global
Mirror
session.
FlashCopy
plays
an
integral
part
of
this
configuration
because
the
set
of
volumes
that
are
FlashCopy
target
volumes
contain
consistent
data.
This
set
of
volumes
is
called
a
consistency
group.
Global Copy
Secondary
FlashCopy
Source
Global Copy
Primary
FlashCopy
Target
Metro
Mirror
Primary
Remote Site
Local Site
Intermediate
Site
(Cascaded Volume)
Metro/Global Mirr
or
A
volumes
Metro Mirror
Secondary
f2c00573
B
volumes
C
volumes
D
volumes
Metro Mirror
Global Mirror
Figure
12.
Metro/Global
Mirror
volume
configuration
120
DS8000
User’s
Guide
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