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I had an interesting discussion recently with a number of my colleagues around the requirement to place additional uplinks (vmnics) on a virtual switch that are not used by iSCSI binding into the 'Unused' state. One would think that it might be useful to team these uplinks, placing some in Standby mode so that in the case of a failure on the active link, the iSCSI traffic could  move to the standby uplink. But the requirement is that other vmnics must be put into the 'Unused' state and not teamed. Why?

This requirement prevents the VMkernel port from floating across uplinks in the case of a failure.  The reason for this is that if the physical NIC loses connectivity, it should be treated as a storage path failure, not a network failure. We want the Pluggable Storage Architecture (PSA) in the VMkernel to handle this event and failover to an alternate path to stay connected to the storage.

This approach enables customers to consider storage resiliency based on multiple paths to the storage, rather than basing it on the number of networks available to a single storage path.

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About the Author

Cormac Hogan

Cormac Hogan is a Senior Staff Engineer in the Office of the CTO in the Storage and Availability Business Unit (SABU) at VMware. He has been with VMware since April 2005 and has previously held roles in VMware’s Technical Marketing and Technical Support organizations. He has written a number of storage related white papers and have given numerous presentations on storage best practices and vSphere storage features. He is also the co-author of the “Essential Virtual SAN” book published by VMware Press.