I/O
to
all
duplex
remote
mirror
and
copy
volumes
on
LSS
pairs
will
be
queued
either
until
a
consistency
group
created
operation
is
run
or
the
consistency
group
timeout
time
expires,
allowing
external
automation
to
use
the
consistency
group
created
operation
to
create
a
dependent
write
consistent
set
of
target
volumes
over
any
number
of
LSS
and
disk
storage
units.
External
automation
or
command-line
interface
commands
can
issue
a
″
freeze
″
to
all
LSS
pairs
that
relate
to
the
application,
affecting
the
set
of
source
volumes
in
the
consistency
group.
The
freeze
operation
causes
the
source
volumes
to
suspend
and
their
associated
paths
to
end.
Therefore,
all
associated
updates
at
the
recovery
site
are
halted,
resulting
in
a
consistent
data
checkpoint.
The
automation
program
is
not
a
part
of
the
software
provided
with
the
storage
unit;
it
must
be
supplied
by
the
user.
However,
IBM
has
offerings
to
assist
with
this
automation.
For
more
information,
contact
your
IBM
storage
representative.
A
consistency
grouping
timeout
function
gives
automation
software
the
time
to
issue
the
automated
requests
to
ensure
consistency.
The
consistency
grouping
timeout
is
a
value
that
specifies
the
length
of
time
that
the
volume
remains
in
long-busy
(unavailable)
following
an
error.
You
can
change
this
value
by
accessing
Copy
Services
functions
from
the
Web
interface
(DS
Storage
Manager
)
and
navigating
to
the
Paths
page
and
then
to
the
LSS
options
page.
The
default
value
for
this
parameter
is
set
to
two
minutes.
Note:
The
consistency
group
option
is
not
required
for
Global
Mirror
or
for
Global
Copy.
Global
Copy
always
keeps
a
inconsistent
copy
of
the
volumes
at
the
recovery
site.
The
volume
pairs
become
consistent
only
when
all
updates
are
transmitted
and
copied
to
the
recovery
site
while
the
application
write
operations
are
quiesced.
Global
Mirror
uses
a
function
called
a
session
to
control
the
formation
of
consistency
groups.
(A
session
is
a
collection
of
volumes
across
multiple
storage
units
that
are
managed
together
to
create
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.
The
following
describes
the
behavior
of
these
volume
pairs
when
an
error
occurs
that
affects
a
volume
in
a
consistency
group:
v
Without
the
consistency
group
option
enabled,
the
storage
unit
causes
the
volume
where
the
error
is
detected
to
enter
a
suspended
state,
but
updates
to
that
volume
are
still
allowed.
v
With
the
consistency
group
option
enabled,
the
volume
becomes
suspended
and
additionally
enters
a
long-busy
state.
Updates
are
not
possible
to
volumes
from
the
source
LSS
to
target
LSS
that
are
sharing
the
same
path.
A
critical
mode
determines
the
behavior
of
the
remote
mirror
and
copy
pairs
or
consistency
groups
after
a
failure
in
communication
between
the
source
and
target
storage
units
when
all
the
paths
between
a
pair
are
lost.
You
can
enable
this
mode
also
by
accessing
Copy
Services
functions
from
the
DS
Storage
Manager
and
by
navigating
to
the
Paths
page
and
then
to
the
LSS
options
page.
Failover
and
failback
operations
The
failover
operation
is
the
process
of
switching
production
to
a
backup
facility
(normally
your
recovery
site).
A
failback
operation
is
the
process
of
returning
production
to
its
original
location
after
a
disaster
or
a
scheduled
maintenance
period.
Chapter
1.
Introduction
15
Summary of Contents for System storage DS6000 Series
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