<s>
In	O
computing	O
the	O
SCSI	B-Protocol
RDMA	I-Protocol
Protocol	I-Protocol
(	O
SRP	O
)	O
is	O
a	O
protocol	O
that	O
allows	O
one	O
computer	O
to	O
access	O
SCSI	B-Architecture
devices	O
attached	O
to	O
another	O
computer	O
via	O
remote	B-General_Concept
direct	I-General_Concept
memory	I-General_Concept
access	I-General_Concept
(	O
RDMA	B-General_Concept
)	O
.	O
</s>
<s>
The	O
SRP	O
protocol	O
is	O
also	O
known	O
as	O
the	O
SCSI	B-Architecture
Remote	O
Protocol	O
.	O
</s>
<s>
The	O
use	O
of	O
RDMA	B-General_Concept
makes	O
higher	O
throughput	O
and	O
lower	O
latency	O
possible	O
than	O
what	O
is	O
generally	O
available	O
through	O
e.g.	O
</s>
<s>
Though	O
the	O
SRP	O
protocol	O
has	O
been	O
designed	O
to	O
use	O
RDMA	B-General_Concept
networks	O
efficiently	O
,	O
it	O
is	O
also	O
possible	O
to	O
implement	O
the	O
SRP	O
protocol	O
over	O
networks	O
that	O
do	O
not	O
support	O
RDMA	B-General_Concept
.	O
</s>
<s>
As	O
with	O
the	O
ISCSI	B-Protocol
Extensions	I-Protocol
for	I-Protocol
RDMA	I-Protocol
(	O
iSER	O
)	O
communication	O
protocol	O
,	O
there	O
is	O
the	O
notion	O
of	O
a	O
target	O
(	O
a	O
system	O
that	O
stores	O
the	O
data	O
)	O
and	O
an	O
initiator	O
(	O
a	O
client	O
accessing	O
the	O
target	O
)	O
with	O
the	O
target	O
initiating	O
data	O
transfers	O
.	O
</s>
<s>
In	O
other	O
words	O
,	O
when	O
an	O
initiator	O
writes	O
data	O
to	O
a	O
target	O
,	O
the	O
target	O
executes	O
an	O
RDMA	B-General_Concept
read	O
to	O
fetch	O
the	O
data	O
from	O
the	O
initiator	O
and	O
when	O
a	O
user	O
issues	O
a	O
SCSI	B-Architecture
read	O
command	O
,	O
the	O
target	O
sends	O
an	O
RDMA	B-General_Concept
write	O
to	O
the	O
initiator	O
.	O
</s>
<s>
On	O
Linux	O
,	O
there	O
are	O
two	O
SRP	O
and	O
two	O
iSER	O
storage	O
target	O
implementations	O
available	O
that	O
run	O
inside	O
the	O
kernel	O
(	O
SCST	B-Application
and	O
LIO	B-Application
)	O
and	O
an	O
iSER	O
storage	O
target	O
implementation	O
that	O
runs	O
in	O
user	O
space	O
(	O
STGT	O
)	O
.	O
</s>
<s>
Measurements	O
have	O
shown	O
that	O
the	O
SCST	B-Application
SRP	O
target	O
has	O
a	O
lower	O
latency	O
and	O
a	O
higher	O
bandwidth	O
than	O
the	O
STGT	O
iSER	O
target	O
.	O
</s>
<s>
This	O
is	O
probably	O
because	O
the	O
RDMA	B-General_Concept
communication	O
overhead	O
is	O
lower	O
for	O
a	O
component	O
implemented	O
in	O
the	O
Linux	O
kernel	O
than	O
for	O
a	O
user	O
space	O
Linux	O
process	O
,	O
and	O
not	O
because	O
of	O
protocol	O
differences	O
.	O
</s>
<s>
The	O
IBM	O
POWER	O
virtual	O
SCSI	B-Architecture
client	O
driver	O
for	O
Linux	O
(	O
ibmvscsi	O
)	O
,	O
available	O
since	O
January	O
2008	O
(	O
kernel	O
version	O
2.6.24	O
)	O
.	O
</s>
<s>
Virtual	O
SCSI	B-Architecture
allows	O
client	O
logical	O
partitions	O
to	O
access	O
I/O	O
devices	O
(	O
disk	O
,	O
CD	O
,	O
and	O
tape	O
)	O
that	O
are	O
owned	O
by	O
another	O
logical	O
partition	O
.	O
</s>
<s>
The	O
SCST	B-Application
SRP	O
target	O
implementation	O
.	O
</s>
<s>
This	O
is	O
a	O
mature	O
SRP	O
target	O
implementation	O
available	O
since	O
2008	O
via	O
both	O
SCST	B-Application
and	O
OFED	O
.	O
</s>
<s>
Linux	O
LIO	B-Application
SRP	O
target	O
,	O
available	O
since	O
January	O
2012	O
(	O
kernel	O
version	O
3.3	O
)	O
,	O
based	O
on	O
the	O
SCST	B-Application
SRP	O
target	O
.	O
</s>
<s>
The	O
IBM	O
POWER	O
virtual	O
SCSI	B-Architecture
target	O
driver	O
(	O
ibmvstgt	O
)	O
,	O
available	O
since	O
January	O
2008	O
(	O
kernel	O
version	O
2.6.24	O
)	O
.	O
</s>
