Improve fault tolerance in cluster server for iSCSI

You can improve fault tolerance in a highly networked environment like an iSCSI cluster server by using NIC teaming.

An iSCSI cluster server has a complex networking structure because each cluster uses no less than three networks to tie everything together.

The three networks are:

The iSCSI SAN. This should be on a physically independent network, and the network interface card (NIC) should not be enabled for cluster use.

A public network. This allows the cluster to communicate with external clients.

A private network. This network communicates among the clusters and must be a physically separate network.

Each node in the cluster needs a separate network interface card to support each network.

NIC teaming, an obvious way to improve fault tolerance in a highly networked environment like this, binds two physical NICs together into a single logical NIC and eliminates a single point of failure in the network.

However, Cluster Server for iSCSI only supports NIC teaming on the public network. It does not support it on a storage area network or private network. To get more fault tolerance on the SAN in an iSCSI cluster server, Microsoft recommends using either MS MPIO (multipath I/O) or Multiple Connections per Session (MCS from the iSCSI specification) on the SAN.

Both MCS and MPIO allow failover among multiple NICs and both of them can support I/O load balancing as well. MCS offers multiple TCP/IP connections between the server and the storage device during the same iSCSI session. These can be on different physical links as well. MPIO lets the server log multiple sessions to the storage array.

Microsoft discusses this in a TechNet article, "Server Clusters Network Configuration Best Practices for Windows 2000 and Windows Server 2003" located here: www.microsoft.com/technet/prodtechnol/windowsserver2003/technologies/clustering/clstntbp.mspx.


Rick Cook has been writing about mass storage since the days when the term meant an 80 K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last 20 years he has been a freelance writer specializing in storage and other computer issues.
This was first published in October 2005

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