<s>
In	O
virtualization	B-General_Concept
,	O
input/output	O
virtualization	B-General_Concept
(	O
I/O	B-Protocol
virtualization	I-Protocol
)	O
is	O
a	O
methodology	O
to	O
simplify	O
management	O
,	O
lower	O
costs	O
and	O
improve	O
performance	O
of	O
servers	B-Application
in	O
enterprise	O
environments	O
.	O
</s>
<s>
I/O	B-Protocol
virtualization	I-Protocol
environments	O
are	O
created	O
by	O
abstracting	O
the	O
upper	B-Protocol
layer	I-Protocol
protocols	I-Protocol
from	O
the	O
physical	B-Application
connections	I-Application
.	O
</s>
<s>
The	O
technology	O
enables	O
one	O
physical	O
adapter	O
card	O
to	O
appear	O
as	O
multiple	O
virtual	B-Application
network	B-Protocol
interface	I-Protocol
cards	I-Protocol
(	O
vNICs	B-Protocol
)	O
and	O
virtual	B-Application
host	B-Architecture
bus	I-Architecture
adapters	I-Architecture
(	O
vHBAs	B-Protocol
)	O
.	O
</s>
<s>
Virtual	B-Application
NICs	O
and	O
HBAs	O
function	O
as	O
conventional	O
NICs	O
and	O
HBAs	O
,	O
and	O
are	O
designed	O
to	O
be	O
compatible	O
with	O
existing	O
operating	B-General_Concept
systems	I-General_Concept
,	O
hypervisors	B-Operating_System
,	O
and	O
applications	O
.	O
</s>
<s>
To	O
networking	O
resources	O
(	O
LANs	B-General_Concept
and	O
SANs	O
)	O
,	O
they	O
appear	O
as	O
normal	O
cards	O
.	O
</s>
<s>
In	O
the	O
physical	O
view	O
,	O
virtual	B-Application
I/O	O
replaces	O
a	O
server	O
’s	O
multiple	O
I/O	O
cables	O
with	O
a	O
single	O
cable	O
that	O
provides	O
a	O
shared	O
transport	O
for	O
all	O
network	B-Architecture
and	O
storage	O
connections	O
.	O
</s>
<s>
That	O
cable	O
(	O
or	O
commonly	O
two	O
cables	O
for	O
redundancy	O
)	O
connects	O
to	O
an	O
external	O
device	O
,	O
which	O
then	O
provides	O
connections	O
to	O
the	O
data	B-Operating_System
center	I-Operating_System
networks	O
.	O
</s>
<s>
Server	O
I/O	O
is	O
a	O
critical	O
component	O
to	O
successful	O
and	O
effective	O
server	O
deployments	O
,	O
particularly	O
with	O
virtualized	B-General_Concept
servers	B-Application
.	O
</s>
<s>
To	O
accommodate	O
multiple	O
applications	O
,	O
virtualized	B-General_Concept
servers	B-Application
demand	O
more	O
network	B-Architecture
bandwidth	O
and	O
connections	O
to	O
more	O
networks	O
and	O
storage	O
.	O
</s>
<s>
According	O
to	O
a	O
survey	O
,	O
75%	O
of	O
virtualized	B-General_Concept
servers	B-Application
require	O
7	O
or	O
more	O
I/O	O
connections	O
per	O
device	O
,	O
and	O
are	O
likely	O
to	O
require	O
more	O
frequent	O
I/O	O
reconfigurations	O
.	O
</s>
<s>
In	O
virtualized	B-General_Concept
data	B-Operating_System
centers	I-Operating_System
,	O
I/O	O
performance	O
problems	O
are	O
caused	O
by	O
running	O
numerous	O
virtual	B-Architecture
machines	I-Architecture
(	O
VMs	O
)	O
on	O
one	O
server	O
.	O
</s>
<s>
In	O
early	O
server	B-General_Concept
virtualization	I-General_Concept
implementations	O
,	O
the	O
number	O
of	O
virtual	B-Architecture
machines	I-Architecture
per	O
server	O
was	O
typically	O
limited	O
to	O
six	O
or	O
less	O
.	O
</s>
<s>
But	O
it	O
was	O
found	O
that	O
it	O
could	O
safely	O
run	O
seven	O
or	O
more	O
applications	O
per	O
server	O
,	O
often	O
using	O
80	O
percent	O
of	O
total	O
server	O
capacity	O
,	O
an	O
improvement	O
over	O
the	O
average	O
5	O
to	O
15	O
percent	O
utilized	O
with	O
non-virtualized	O
servers	B-Application
.	O
</s>
<s>
However	O
,	O
increased	O
utilization	O
created	O
by	O
virtualization	B-General_Concept
placed	O
a	O
significant	O
strain	O
on	O
the	O
server	O
’s	O
I/O	O
capacity	O
.	O
</s>
<s>
Network	B-Architecture
traffic	O
,	O
storage	O
traffic	O
,	O
and	O
inter-server	O
communications	O
combine	O
to	O
impose	O
increased	O
loads	O
that	O
may	O
overwhelm	O
the	O
server	O
's	O
channels	O
,	O
leading	O
to	O
backlogs	O
and	O
idle	O
CPUs	B-Device
as	O
they	O
wait	O
for	O
data	O
.	O
</s>
<s>
Virtual	B-Application
I/O	O
addresses	O
performance	O
bottlenecks	O
by	O
consolidating	O
I/O	O
to	O
a	O
single	O
connection	O
whose	O
bandwidth	O
ideally	O
exceeds	O
the	O
I/O	O
capacity	O
of	O
the	O
server	O
itself	O
,	O
thereby	O
ensuring	O
that	O
the	O
I/O	O
link	O
itself	O
is	O
not	O
a	O
bottleneck	O
.	O
</s>
<s>
That	O
bandwidth	O
is	O
then	O
dynamically	O
allocated	O
in	O
real	O
time	O
across	O
multiple	O
virtual	B-Application
connections	O
to	O
both	O
storage	O
and	O
network	B-Architecture
resources	O
.	O
</s>
<s>
Virtual	B-Application
I/O	O
systems	O
that	O
include	O
quality	O
of	O
service	O
(	O
QoS	O
)	O
controls	O
can	O
also	O
regulate	O
I/O	O
bandwidth	O
to	O
specific	O
virtual	B-Architecture
machines	I-Architecture
,	O
thus	O
ensuring	O
predictable	O
performance	O
for	O
critical	O
applications	O
.	O
</s>
<s>
QoS	O
thus	O
increases	O
the	O
applicability	O
of	O
server	B-General_Concept
virtualization	I-General_Concept
for	O
both	O
production	O
server	O
and	O
end-user	O
applications	O
.	O
</s>
<s>
Management	O
agility	O
:	O
By	O
abstracting	O
upper	B-Protocol
layer	I-Protocol
protocols	I-Protocol
from	O
physical	B-Application
connections	I-Application
,	O
I/O	B-Protocol
virtualization	I-Protocol
provides	O
greater	O
flexibility	O
,	O
greater	O
utilization	O
and	O
faster	O
provisioning	O
when	O
compared	O
to	O
traditional	O
NIC	O
and	O
HBA	B-Architecture
card	O
architectures	O
.	O
</s>
<s>
Virtual	B-Application
I/O	O
technologies	O
can	O
be	O
dynamically	O
expanded	O
and	O
contracted	O
(	O
versus	O
traditional	O
physical	O
I/O	O
channels	O
that	O
are	O
fixed	O
and	O
static	O
)	O
,	O
and	O
usually	O
replace	O
multiple	O
network	B-Architecture
and	O
storage	O
connections	O
to	O
each	O
server	O
with	O
a	O
single	O
cable	O
that	O
carries	O
multiple	O
traffic	O
types	O
.	O
</s>
<s>
Because	O
configuration	O
changes	O
are	O
implemented	O
in	O
software	O
rather	O
than	O
hardware	O
,	O
time	O
periods	O
to	O
perform	O
common	O
data	B-Operating_System
center	I-Operating_System
tasks	O
–	O
such	O
as	O
adding	O
servers	B-Application
,	O
storage	O
or	O
network	B-Architecture
connectivity	O
–	O
can	O
be	O
reduced	O
from	O
days	O
to	O
minutes	O
.	O
</s>
<s>
Reduced	O
cost	O
:	O
Virtual	B-Application
I/O	O
lowers	O
costs	O
and	O
enables	O
simplified	O
server	O
management	O
by	O
using	O
fewer	O
cards	O
,	O
cables	O
,	O
and	O
switch	O
ports	O
,	O
while	O
still	O
achieving	O
full	O
network	B-Architecture
I/O	O
performance	O
.	O
</s>
<s>
It	O
also	O
simplifies	O
data	B-Operating_System
center	I-Operating_System
network	B-Architecture
design	O
by	O
consolidating	O
and	O
better	O
utilizing	O
LAN	B-General_Concept
and	O
SAN	O
network	B-Architecture
switches	O
.	O
</s>
<s>
Reduced	O
cabling	O
:	O
In	O
a	O
virtualized	B-General_Concept
I/O	O
environment	O
,	O
only	O
one	O
cable	O
is	O
needed	O
to	O
connect	O
servers	B-Application
to	O
both	O
storage	O
and	O
network	B-Architecture
traffic	O
.	O
</s>
<s>
This	O
can	O
reduce	O
data	B-Operating_System
center	I-Operating_System
server-to-network	O
,	O
and	O
server-to-storage	O
cabling	O
within	O
a	O
single	O
server	O
rack	O
by	O
more	O
than	O
70	O
percent	O
,	O
which	O
equates	O
to	O
reduced	O
cost	O
,	O
complexity	O
,	O
and	O
power	O
requirements	O
.	O
</s>
<s>
Increased	O
density	O
:	O
I/O	B-Protocol
virtualization	I-Protocol
increases	O
the	O
practical	O
density	O
of	O
I/O	O
by	O
allowing	O
more	O
connections	O
to	O
exist	O
within	O
a	O
given	O
space	O
.	O
</s>
<s>
This	O
in	O
turn	O
enables	O
greater	O
utilization	O
of	O
dense	O
1U	O
high	O
servers	B-Application
and	O
blade	O
servers	B-Application
that	O
would	O
otherwise	O
be	O
I/O	O
constrained	O
.	O
</s>
<s>
Blade	O
server	O
chassis	O
enhance	O
density	O
by	O
packaging	O
many	O
servers	B-Application
(	O
and	O
hence	O
many	O
I/O	O
connections	O
)	O
in	O
a	O
small	O
physical	O
space	O
.	O
</s>
<s>
Virtual	B-Application
I/O	O
consolidates	O
all	O
storage	O
and	O
network	B-Architecture
connections	O
to	O
a	O
single	O
physical	O
interconnect	O
,	O
which	O
eliminates	O
any	O
physical	O
restrictions	O
on	O
port	O
counts	O
.	O
</s>
<s>
Virtual	B-Application
I/O	O
also	O
enables	O
software-based	O
configuration	O
management	O
,	O
which	O
simplifies	O
control	O
of	O
the	O
I/O	O
devices	O
.	O
</s>
