HP Cisco MDS 9020 - Fabric Switch Configuration Manual page 1037

Chapter 42 Configuring iSCSI
S e n d d o c u m e n t a t i o n c o m m e n t s t o m d s f e e d b a c k - d o c @ c i s c o . c o m
Figure 42-13
Figure 42-13
Pass -Thru
iSCSI initiator
Command1
iSCSI Data-
in PDU #1,
DSlen = 1KB
iSCSI
Data-in
PDU #2
iSCSI
Data-in
PDU #16
Response1
Command2
Table 42-1
Table 42-1
Mode
Pass-thru
Store-and-forward
Cut-thru
OL-16184-01, Cisco MDS SAN-OS Release 3.x
compares the messages exchanged by the iSCSI routing modes.
iSCSI Routing Modes
MDS FC Target
Command
Data1
Data2
Data16
Status
compares the advantages and disadvantages of the different iSCSI routing modes.
Comparison of iSCSI Routing Modes
Advantages
Low-latency
Data digest can be used
Higher data transfer
performance
Improved read performance
over store-and-forward
Store -Forward
iSCSI initiator MDS FC Target
Command1
Command
Data1
Wait for all
Data to
arrive
Data16
TCP part 1
contains iSCSI
Data-in PDU #1
DSlen = 16KB
TCP part 2
TCP part 16
Status
Response1
Command2
Disadvantages
Lower data transfer performance.
Data digest cannot be used.
If the Fibre Channel target sent read data for
different commands interchangeably, data of the
first command is forwarded in cut-thru mode but
the data of subsequent commands is buffered
and the behavior is the same as
store-and-forward mode.
Data digest cannot be used.
Cisco MDS 9000 Family CLI Configuration Guide
Configuring iSCSI
Cut -Thru
iSCSI initiator MDS
Command1
Command
TCP part 1
contains iSCSI
Data-in PDU #1
Data frame is
DSlen = 16KB
forwarded as
Data2
it is received
TCP part 2
Data16
TCP part 16
Status
Response1
Command2
FC Targ
Data1
42-29