Determine the need for an IP storage network. The first purchase consideration should be to evaluate the need for an IP storage network in the first place. If a site already deploys 100% FC, it may not make sense to add IP storage to the mix. It's another storage infrastructure that needs to be implemented and managed. However, the price/performance tradeoff can be compelling; by implementing an inexpensive and well-understood IP storage infrastructure, many more servers can be cost-effectively interconnected to the fabric, and this in turn can dramatically improve server resource availability for the entire workgroup or organization -- a good first step in server/storage consolidation. Also consider the applications that will run on the IP SAN. Some applications are better-suited for an IP SAN, while others may require an FC SAN. Lab testing can help identify any potential application compatibility problems.
Consider the logical separation points. While smaller organizations could deploy IP storage networks only, larger IT departments with a current FC investment must decide how IP storage fits in the overall storage picture. For example, it might be prudent to place user data on IP storage, while mission-critical applications and data remain on FC. Similarly, IP SANs may be appealing in remote offices where a smaller staff can easily be supported, and storage data can be exchanged with the main data center across the Internet. IP switches and routers should be selected with such criteria in mind. Industry experts note other technical purchase considerations including SAN segmentation support and cross domain inter fabric routing; including mapping zones across SAN segments. Virtualization is often used to segregate IP SANs (Cisco has coined the term VSAN).
Consider IP SAN security features. The ubiquitous nature of IP can impair IP SAN security. It is important to keep the IP SAN logically separated from the rest of the user LAN. Otherwise it is possible that sensitive corporate data may "leak out" across the LAN and onto the Internet unexpectedly. In addition to good IP SAN planning, you should also evaluate the authorization and authentication capabilities of an IP switch or router to ensure that no unauthorized users can access the IP SAN. For example, Brocade's FC4-16IP Blade for 48000 Director includes RADIUS. By comparison, Cisco's 9216A and 9216i Multilayer Fabric Switches includes support for IPsec, Internet Key Exchange (IKE), and virtual SANs (VSANs).
Consider the ports and connectivity features. Since iSCSI is often implemented to supplement a FC SAN, the switch and router hardware will implement both IP and FC ports on the same physical device. Evaluate the available ports and their performance to be sure that an iSCSI investment will offer adequate expandability. For example, Brocade's iSCSI gateway combines two Gigabit Ethernet ports and two 2 Gb/s FC ports into a single device -- this approach is adept at linking servers with both iSCSI and FC storage systems. Also pay attention to the device's protocol support, and translations between protocols should accommodate your specific needs. For example, an IP switch or router may handle translations like iSCSI to FCP, FCP to FCIP, FCP to iFCP, FCP to FICON, FCP to SRP, and so on. Advanced features like active/active clustered failover, failback, and multipathing capabilities all help to improve the reliability and availability of the IP SAN.
Consider the available management tools. All IP switches and routers will provide some type of management software, but it's important to evaluate the effectiveness and flexibility of the software before making a purchase decision. Tools should generally allow for device configuration and maintenance. Management tools may allow performance monitoring for resource utilization analysis and service level management. Intelligent health monitoring features can identify potential faults and alert a technician. Enhanced features like ISL trunking aid inter-switch performance and port consolidation. Today, management tools are increasingly heterogeneous, supporting multiple vendors' devices through a single console.
Consider WAN features like compression and acceleration. IP devices intended to operate over WAN connections may include features designed to optimize bandwidth. FCIP compression reduces redundant data, shrinking the shear amount of data passed across the WAN. Acceleration features like FCIP write acceleration and FCIP tape acceleration improve storage traffic across distance by eliminating the latency caused by command acknowledgements. For example, Cisco's MDS 9000 IP Storage Services Modules claim compression ratios of 2:1 to 30:1, while supporting both FCIP write acceleration and FCIP tape acceleration.
The IP storage switch and router specifications page in this chapter covers the following products: