Switches segregate network traffic, ensuring that data on one network segment is only passed to the segment that leads to an intended destination. This helps to organize the network and reduce unneeded traffic. Switches are particularly crucial in a storage area network (SAN) and are used to interconnect storage devices into the overall SAN fabric. SAN upgrades often involve changes to the switch fabric. For example, additional switches can connect more storage devices or establish redundant connections between them, faster switches can accelerate SAN performance, and large switches can be installed to consolidate an assortment of disparate switch devices.
Consequently, choosing a switch can be a surprisingly complex task: There are many switches to choose from, and the actual choice of an enterprise switch demands careful consideration of issues like speed, performance, port count and interoperability. Now that you've reviewed the essential issues involved in any SAN upgrade, this segment will first focus on specific considerations for enterprise-class switches. After that, you'll also find a series of specifications to help make on-the-spot product comparisons between vendors, including Brocade Communications Systems Inc., Cisco Systems Inc. and McData Corp. (now part of Brocade).
Choose the appropriate SAN technology. Select the connectivity that matches your current SAN. Most conventional SAN implementations use Fibre Channel connectivity, though mainframe-based SANs will typically employ FICON (fiber connectivity) ports. ISCSI is growing in importance, but iSCSI is normally deployed on a regular Ethernet network --- IP storage uses Ethernet switches to segment the SAN traffic from the remainder of the user network.
Select an adequate port count and speed. There should be enough switch ports available to accommodate existing storage devices and allow headroom for reasonable storage growth into the future. In addition, many SAN configurations commit multiple switch ports to each connection. Multiport setups help performance through trunking and improve reliability through redundancy and failover capability. This helps to eliminate single points of failure in the fabric that might render some storage inaccessible. Port speed is another important consideration. Analysts suggest adopting switches with 4 Gbit Fibre Channel ports today. Older 2 Gbit (and even 1 Gbit) Fibre Channel ports are readily available and inexpensive, but performance-hungy SANs will benefit from the higher port speed, and the faster ports should still be backward compatible with slower devices. ISCSI SANs will benefit from Gigabit Ethernet speeds or faster.
Consider a switch consolidation strategy. Each new switch added to the SAN will impact reliability, performance and management. Eventually, a lot of little switches will become difficult to troubleshoot and impossible to manage. The cumulative delay of interswitch links (ISLs) can slow communication across the fabric and impair performance. Analysts recommend consolidating smaller switches into fewer, larger switches, such as directors, wherever possible. This improves switching performance and greatly simplifies management because many more ports are managed through a single software tool.
Settle on a single vendor. Many organizations work with a variety of switch vendors. While such competition can help save on capital expenditures, experts note that this may actually be a false economy. Mixing and matching switches may actually result in wasted money because the features and capabilities of one switch may not be supported by other switches from different manufacturers. For example, mixing dissimilar switches may compromise key security features that might not be supported across all of the switches in a SAN. Settle on Brocade, Cisco or another vendor of choice. If you choose to eliminate secondary switch vendors, approach the process in phases to reduce SAN disruptions.
Confirm interoperability in the storage environment. While switches should generally work together, it's still important to verify interoperability with other switches and storage systems early in the acquisition process. The vendor's product compatibility matrix is typically a good place to start. A vendor can usually provide specific details and assistance with compatibility testing if the need arises. As a rule, switch consolidation can ease interoperability issues because there are fewer switches (and switch vendors) involved in the fabric.
Consider specialized application support. Understand any applications that depend on the SAN environment and evaluate the importance of application support. For example, switches that are designed to accommodate enterprise resource planning (ERP), data warehousing, backup, mirroring/snapshots and other key tasks may have a profound impact on the performance of those applications. Lab testing and evaluation prior to purchase can help to identify the suitability of a switch for a particular application.
Consider other switch features and management capabilities. Beyond the port attributes, it's important to weigh the entire suite of switch features. For example, other feature areas of the switch may include security, performance monitoring, ISL trunking, call-home maintenance and a variety of high-availability capabilities. Pay particular attention to expandability options, especially if you plan to consolidate multiple switches into a larger switch or director. Also, look for high-end intelligent features, such as virtualization or data replication.
The enterprise switch product specifications page in this chapter covers the following products:
Brocade Communications Systems Inc.; SilkWorm 48000 director
Brocade Communications Systems Inc.; Mi10K (formerly McData)
Brocade Communications Systems Inc.; M6140 (formerly McData)
Cisco Systems Inc.; MDS 9124 Multilayer Fabric Switch
Cisco Systems Inc.; MDS 9506 Multilayer Director
Cisco Systems Inc.; MDS 9509 Multilayer Director
Cisco Systems Inc.; MDS 9513 Multilayer Director
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