Chapter
2.
SAN
Volume
Controller
overview
The
SAN
Volume
Controller
combines
hardware
and
software
into
a
comprehensive,
modular
appliance
that
uses
symmetric
virtualization.
Symmetric
virtualization
is
achieved
by
creating
a
pool
of
managed
disks
(MDisks)
from
the
attached
storage
subsystems.
Those
storage
systems
are
then
mapped
to
a
set
of
virtual
disks
(VDisks)
for
use
by
attached
host
systems.
System
administrators
can
view
and
access
a
common
pool
of
storage
on
the
SAN.
This
lets
the
administrators
use
storage
resources
more
efficiently
and
provides
a
common
base
for
advanced
functions.
A
SAN
is
a
high-speed
fibre-channel
network
that
connects
host
systems
and
storage
devices.
It
allows
a
host
system
to
be
connected
to
a
storage
device
across
the
network.
The
connections
are
made
through
units
such
as
routers,
gateways,
hubs,
and
switches.
The
area
of
the
network
that
contains
these
units
is
known
as
the
fabric
of
the
network.
The
SAN
Volume
Controller
is
analogous
to
a
logical
volume
manager
on
a
SAN.
The
SAN
Volume
Controller
performs
the
following
functions
for
the
SAN
storage
that
it
controls:
v
Creates
a
single
pool
of
storage
v
Provides
logical
unit
virtualization
v
Manages
logical
volumes
v
Provides
the
following
advanced
functions
for
the
SAN:
–
Large
scalable
cache
–
Copy
Services
-
FlashCopy
®
(point-in-time
copy)
-
Metro
Mirror
(synchronous
copy)
-
Global
Mirror
(asynchronous
copy)
-
Data
migration
–
Space
management
-
Mapping
that
is
based
on
desired
performance
characteristics
-
Metering
of
service
quality
Each
SAN
Volume
Controller
node
is
a
rack-mounted
unit
that
you
can
install
in
a
standard
Electrical
Industries
Alliance
(EIA)
19-inch
rack.
The
nodes
are
always
installed
in
pairs,
with
one-to-four
pairs
of
nodes
constituting
a
cluster
.
Each
pair
of
nodes
is
known
as
an
I/O
group
.
All
I/O
operations
that
are
managed
by
the
nodes
in
an
I/O
group
are
cached
on
both
nodes.
Each
virtual
volume
is
defined
to
an
I/O
group.
I/O
groups
take
the
storage
that
is
presented
to
the
SAN
by
the
storage
subsystems
as
MDisks
and
translates
the
storage
into
logical
disks,
known
as
VDisks,
that
are
used
by
applications
on
the
hosts.
Each
node
must
reside
in
only
one
I/O
group
and
provide
access
to
the
VDisks
in
that
I/O
group.
There
are
four
models
of
SAN
Volume
Controller
nodes:
v
SAN
Volume
Controller
2145-8G4
©
Copyright
IBM
Corp.
2003,
2007
3
Summary of Contents for 2145UPS-1U
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