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By Henry Baltazar  |  Posted 2004-12-13 Print this article Print
 
 
 
 
 
 
 


The purpose of san routers is not only to route traffic from one SAN island to another but also to keep SAN islands from flooding each other with communication traffic.

In Brocades SilkWorm Multiprotocol Router solution, routers are inserted between SAN islands and act as virtual switches. (Brocade calls these phantom switches.) Each router can talk with the switches in each SAN island and can get their configuration information. The router uses this information to populate its routing tables. When a device on one SAN island gets permission to talk to a device on another SAN island, the router uses NAT (Network Address Translation) to translate the data as it crosses to the other SAN island.

Brocades SAN routing solution can tolerate duplicate domain identities, eliminating the danger of disruptive fabric reconfiguration events.

Cisco entered the SAN market relatively late, giving it the second-mover advantage. Using technology and ideas from IP networking, Cisco created its VSAN (Virtual SAN) routing technology, called Inter-VSAN, to segregate traffic and make large SANs more efficient.

Unlike other switches on the market, Ciscos Fibre Channel SAN switches have ASICs (application-specific integrated circuits) that sit in the data path and analyze and modify frames at wire speeds. Using these ASICs, the Cisco switches are able to perform tagging at wire speeds on the storage traffic to route frames to the correct SAN islands.

Ciscos VSAN technology adds information to the Fibre Channel frame header to identify the VSANs to which a particular frame belongs. The tagging (where information is added to the Fibre Channel header) done by the Cisco switches is analogous to the tagging process we see in IP VLANs (virtual LANs) today.

The Cisco switches built-in intelligence enables them to detect non-Cisco Fibre Channel switches. When a packet has to be sent to a non-Cisco switch, the ASICs automatically remove the tagged information.

Ciscos VSAN technology was recently chosen by Technical Committee T11 of the International Committee for Information Technology Standards to be the ANSI-approved industry standard for implementing Virtual Fabrics.

However, even with the new standard, we dont expect to see many non-Cisco switches using this technology in the near future. Beyond the challenge of having to develop the technology to implement Virtual Fabrics, the other switch vendors need to contend with the fact that they already have large customer bases that would be less than thrilled with the idea of disruptive mass upgrades.

Click here to read Labs review of Network Appliances Data OnTap 7G, a powerful operating system upgrade that gives NetApp appliances the ability to deliver storage management and virtualization across different vendors storage systems. While VSANs in their current implementation are very good at segregating traffic and improving the efficiency and manageability of large SANs, they cannot handle duplicate domain identities.

In February, Cisco will release a new version of its Inter-VSAN routing technology that will eliminate the need for unique domain identities for each switch.

According to Cisco officials, the Inter-VSAN routing system will let IT managers choose between NAT and non-NAT routing on their SANs.

As SANs continue to grow in size and complexity, SAN routers will become an absolute necessity for all enterprise-class IT environments.

Senior Analyst Henry Baltazar can be reached at henry_baltazar@ziffdavis.com.

Check out eWEEK.coms for the latest news, reviews and analysis on enterprise and small business storage hardware and software.


 
 
 
 
 
 
 
 
 
 
 

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