IP as a viable transport for storage networks

netwrokIP is a viable transport method within SAN’s, as this is a great method for attaching additional client nodes to the SAN without the need of purchasing and installing additional (and expensive) HBA’s for the nodes. iSCSI is one of the tools that enables this to happen. With the use of a software iSCSI initiator, the node can view an assigned iSCSI file system on the storage end and attach to it as a local disk.

Another advantage of IP within a storage network is the utilization of the spanning tree protocol within TCP. Spanning tree monitors redundant links and assigns alternative network paths on demand in the event of a port failure. It also prevents any packet stream from accessing more than one path at a time, preventing packet or broadcast flooding in the network. Think of it as a traffic cop. Spanning Tree is valuable for SAN traffic, as it will keep the data going in the event of a link failure. This is known as transparent bridging in the text (p.81). With Fiber Channel, there is usually a second fiber switch that will enable continuity of the connection if the other goes down. It seems to me that IP can provide more links to the target.

Spanning Tree is being replaced presently in a few organizations by the new Flex Link protocol:

“Flex Link is a Layer 2 availability feature that can co-exist with spanning tree. This enhancement allows a convergence time of less than 50 milliseconds. In addition, this convergence time remains consistent regardless of the number of VLANs or MAC addresses configured on switch uplink ports. It is a pair of a Layer 2 interfaces, either switchports or port channels, that are configured to act as a backup to another Layer 2 interface. The feature provides an alternative solution to the spanning tree protocol (STP), and it allows users to turn off STP and still provide basic link redundancy”

Reference:

Cisco. (2009). How to configure a Flex Link for link-level redundancy in Cisco Catalyst switches that run Cisco IOS. Retrieved July 16, 2009 from http://supportwiki.cisco.com/ViewWiki/index.php/How_to_configure_a_Flex_Link_for_link-level_redundancy_in_Cisco_Catalyst_switches_that_run_Cisco_IOS

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About Steve J
M.A. Information Systems

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