Multipathing for Software iSCSI

see also:http://www.vmware.com/files/pdf/techpaper/vmware-multipathing-configuration-software-iSCSI-port-binding.pdf

好文：http://bbs.vmsky.com/thread-35898-1-1.html

http://communities.vmware.com/thread/397882?start=0  通常iscsi不使用LACP或者NIC Teaming

Multipathing between a server and storage array provides the ability to load-balance between paths when all
paths are present and to handle failures of a path at any point between the server and the storage. Multipathing
is a de facto standard for most Fibre Channel SAN environments. In most software iSCSI environments,
multipathing is possible at the VMkernel network adapter level, but not the default configuration.
In a VMware vSphere? environment, the default iSCSI configuration for VMware? ESXi? servers creates only one
path from the software iSCSI adapter (vmhba) to each iSCSI target. To enable failover at the path level and to
load-balance I/O traffic between paths, the administrator must configure port binding to create multiple paths
between the software iSCSI adapters on ESXi servers and the storage array.
Without port binding, all iSCSI LUNs will be detected using a single path per target. By default, ESX will use
only one vmknic as egress port to connect to each target, and you will be unable to use path failover or to loadbalance
I/O between different paths to the iSCSI LUNs. This is true even if you have configured network adapter
teaming using more than one uplink for the VMkernel port group used for iSCSI. In case of simple network
adapter teaming, traffic will be redirected at the network layer to the second network adapter during
connectivity failure through the first network card, but failover at the path level will not be possible, nor will
load balancing between multiple paths.
Some of the user guides and documentation refer to vmknic-based software iSCSI multipathing as “port
binding” or simply as “software iSCSI multipathing.” This paper provides an overview of how to enable vmknicbased
software iSCSI multipathing, as well as the procedure by which to verify port binding configuration.

Configuring vmknic-Based iSCSI Multipathing
To enable vmknic-based software iSCSI multipathing, you must:
1.Create two VMkernel port groups and connect one uplink to each of them.
2.Bind each VMkernel network adapter to the software iSCSI adapter. Then run a rediscovery of iSCSI targets to
detect multiple paths to them.
Refer to the following sections to learn the network configuration and port binding procedure required to enable
vmknic-based multipathing for software iSCSI.

注意：可以在不同的vSwitch上建立vmkernel port group.但是如果vmkernel网络适配器是在同一个子网上，则必须建立在同一个vSwitch上。

确保每个vmkernel port group 只对应一个活动的物理网卡。