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
20-49
Cisco MDS 9000 Family Troubleshooting Guide, Release 3.x
OL-9285-05
Chapter 20 Troubleshooting IP Storage Services
iSCSI TCP Performance Issues
CLI Commands Used to Access Performance Data
Use the following CLI commands to access performance data.
•
show iscsi remote-node iscsi-session-detail tcp-parameters
•
show ips stats tcp interface gigabitethernet
slot
/
port
detail
•
show interface iscsi
slot
/
port
•
show interface gigabitethernet
slot/port
•
show interface fc
slot
/
port
•
show iscsi remote-node fcp-session-detail
Understanding TCP Parameters for iSCSI
The default MTU size of an Ethernet network is 1500, while the Fibre Channel networks generally
support maximum frame sizes of 2148 bytes. This means that an iSCSI gateway must divide the Fibre
Channel frames into two TCP segments or IP fragments while transferring from the Fibre Channel side
to the IP side depending on how this division is implemented within the device.
This section refers to the scenario in
Figure 20-13
.
Figure 20-13
IPS Window Scaling
The IPS module adjusts the Receive Data Field Size that it advertises to its Fibre Channel partner,
according to the MTU that is configured on the corresponding Gigabit Ethernet port of an iSCSI client.
If left to the default MTU size, the Fibre Channel frame size from the target device is decreased to match
the maximum Ethernet frame size, so the switching of the packet through the switch is faster. One point
of performance tuning is to increase the MTU of the IP network between the peers.
Jumbo support was enabled for the IPS ports, and the MTU for the VLAN corresponding to these ports
was increased.
The second point of performance tuning is to increase the TCP window size of the iSCSI endpoints.
Depending on the latency between the iSCSI client and the IPS, this will need fine tuning. The switch’s
iSCSI configuration defines the TCP window size in kilobytes.
Catalyst 6000
2/1
2/1
FC 1/3
FC 1/3
C4
C8
E-ISL
FCP
iSCSI/TCP
ESS 2105/F20
MDS 9216_Bottom
1.1(0.133c)
MDS 9216_Top
1.1(0.133c)
Shark-nas
10.48.69.233
Windows 2000/SP3
Cisco iSCSI - 3.1.1
NIC Alacritech TOE
Driver 5.50
10.48.69.250
94230
FC
FC
HBA