Changing Iscsi Interface Parameters And The Impact On Load Balancing; Vrrp Load Balancing Algorithm For Selecting Gigabit Ethernet Interfaces - Cisco MDS 9000 series Configuration Manual

Chapter 4 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
A Gigabit Ethernet interface configured for iSLB can only be in one VRRP group because redirected
Caution
sessions do not carry information about the VRRP IP address or group. This restriction allows the backup
port to uniquely identify the VRRP group to which it belongs.

Changing iSCSI Interface Parameters and the Impact on Load Balancing

All iSCSI interfaces in a VRRP group that has load balancing enabled must have the same interface
VSAN, authentication, proxy initiator mode, and forwarding mode. When you need to change any of
these parameters for the iSCSI interfaces in a VRRP group, you must do so one interface at a time.
During the transition time when the parameter is changed on some interfaces in the VRRP group and not
the others, the master port does not redirect new initiators and instead handles them locally.
Changing the VSAN, proxy initiator, authentication, and forwarding mode for iSCSI interfaces in a
Caution
VRRP group can cause sessions to go down multiple times.

VRRP Load Balancing Algorithm For Selecting Gigabit Ethernet Interfaces

When the VRRP master receives an iSCSI session request from an initiator, it first checks for an existing
mapping to one of the interfaces in that VRRP group. If such a mapping exists, the VRRP master
redirects the initiator to that interface. If no such mapping exists, the VRRP master selects the least
loaded interface and updates the selected interface's load with the initiator's iSLB metric (weight).
Note The VRRP master interface is treated specially and it needs to take a lower load compared to the other
interfaces. This is to account for the redirection work performed by the master interface for every
session. A new initiator is assigned to the master interface only if the following is true for every other
interface:
VRRP backup interface load > [2 * VRRP master interface load + 1]
Example 4-17
•
•
•
•
Example 4-17 Load Distribution with the Default Metric
The follow example output shows the initial load distribution for three initiators with the default load
metric value:
switch# show islb vrrp summary
...
--------------------------------------------------------------------------------
VR Id
--------------------------------------------------------------------------------
M 1
1
1
OL-19525-01,Cisco MDS NX-OS Release 4.2(1)
and Example 4-18
GigabitEthernet2/1.441 is the VRRP master interface for Switch1.
GigabitEthernet2/2.441 is the VRRP backup interface for Switch1.
GigabitEthernet1/1.441 is the VRRP backup interface for Switch2.
GigabitEthernet1/2.441 is the VRRP backup interface for Switch2.
VRRP IP Switch WWN
10.10.122.115 20:00:00:0b:5f:3c:01:80
10.10.122.115 20:00:00:0b:5f:3c:01:80
10.10.122.115 20:00:00:0c:ce:5c:5b:c0
are based on the following configurations:
Ifindex
GigabitEthernet2/1.441
GigabitEthernet2/2.441
GigabitEthernet1/1.441
Cisco MDS 9000 Family NX-OS IP Services Configuration Guide
Configuring iSLB
Load
0
1000
1000
4-51