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
20-57
Cisco MDS 9000 Family Troubleshooting Guide, Release 3.x
OL-9285-05
Chapter 20 Troubleshooting IP Storage Services
iSCSI TCP Performance Issues
Verifying that the Host Is Configured for High MTU or MSS with the CLI
To get the real benefit of an increased MTU and higher Fibre Channel frame size, the path between the
iSCSI client and the IPS iSCSI interface (as well as the host NIC) has to be capable of supporting this
high MTU.
If you do not have access to the host, one way to see if the host is also configured for high MTU/MSS
(as well as the path in the middle) is to check the split packets field in the
show ips stats tcp
display.
However this is a generic display for all TCP sessions. That is, if you have some hosts with high
MTU-capable NICs, and some others without, it may be difficult to assess which is which. (See
Example 20-5
.)
Example 20-5 Sample Output for Low Packet Split Count
MDS_Top#
show ips stats tcp interface gigabitethernet 2/1 detail
(truncated output)
TCP Statistics for port GigabitEthernet2/1
TCP send stats
10 segments, 240 bytes
5 data, 5 ack only packets
0 control (SYN/FIN/RST), 0 probes, 0 window updates
0 segments retransmitted, 0 bytes
0 retransmitted while on ethernet send queue,
0 packets split
...
TCP Active Connections
Local Address Remote Address State Send-Q Recv-Q
10.48.69.250:3260 10.48.69.233:1026 ESTABLISH 0 0
10.48.69.250:3260 10.48.69.233:1040 ESTABLISH 0 0
0.0.0.0:3260 0.0.0.0:0 LISTEN 0 0
Afterward, traffic starts flowing from the FC storage towards the server that is connected via iSCSI to
the IPS.
Example 20-6 Sample Output for Large Packet Split Count
MDS_Top#
show ips stats tcp interface gigabitethernet 2/1 detail
TCP Statistics for port GigabitEthernet2/1
TCP send stats
715535 segments, 943511612 bytes
712704 data, 2831 ack only packets
0 control (SYN/FIN/RST), 0 probes, 0 window updates
0 segments retransmitted, 0 bytes
0 retransmitted while on ethernet send queue,
345477 packets split
...