Weaving SAN fabric proves complicated

It’s quite common for companies to have SANs from different vendors. In some companies, it happens because separate business units make different purchasing decisions; others inherit the IT infrastructure. Still others deliberately acquire the best solution for a specific business problem.

Whatever the reason, companies with a diversified environment have a real need for centralizing storage administration. First, though, they must create a consolidated fabric by connecting existing fabric switches to a common, larger fabric switch or, when traffic volume and size so require, by purchasing a director-class switch for that purpose.

Part of my testing goals was to consolidate the three heterogeneous SANs under the same fabric to give each host access to all the storage arrays. To unify the fabric, the three vendors agreed to create two ISLs (inter-switch links) between their respective SANs and a common pair of fabric switches, and connect them to the EMC pair, which had more free ports.

This minimal objective seemed within easy reach because all our FC switches were essentially Brocade SilkWorm, although rebranded by each vendor. As it turned out, I was wrong. After making the ISL connections, the switches were simply not communicating. The vendors’ technical staffs suggested two possible culprits: different firmware level of the switches and conflicting domain numbers. A phone call to Brocade, however, pointed to dissimilar configuration parameters as the problem.

Finding and adjusting those parameters took some time. Visualize our vendors’ technicians opening the Brocade administrative CLI and patiently checking each of the 50 or more configuration parameters between two switches. After completing that long and tedious task on all switches and resetting the zoning, we finally had a consolidated fabric.

As a result, I was able to register the foreign hosts to each array and create and assign LUNs without fabric restrictions. However, I was still limited to the management tools specific to each vendor for those activities.

We learned a lesson: Getting FC switches to work together is not an exercise in plug and play and can be a challenge even for skilled technicians — even when the switches are all Brocade.