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That is, if your company is an EMC shop. Presently, SAN Architect only works with EMC arrays and switches from Brocade, Inrange, McData and coming soon, Cisco, according to an EMC spokesperson. "At the end of the year, we will support Hitachi Data Systems, HP and IBM," the spokesperson adds. SAN Architect is available as a one-year subscription with an entry-level list price of $2,400.

In February, Computer Associates (CA) acquired Netreon's SANexec Designer and integrated the product into BrightStor. Now called BrightStor SAN Designer, the product contains a large repository of SAN component knowledge and industry best practices. "It works with just about every component out there," says Eric Pitcher, divisional VP of BrightStor solutions.

BrightStor SAN Designer helps a storage architect implement a reliable SAN, and document all components in the SAN, including their make, model and firmware versions. BrightStor SAN Designer can also be used to design a SAN from scratch, to improve a working SAN or to audit a SAN implementation. In its current version, the product follows the best practice guidelines of the individual component manufacturers. In other words, BrightStor SAN Designer can't recommend a Brocade switch over an Inrange switch or vice versa for performance goals. It can only tell you how a specific switch or other SAN component will work with another SAN component. However, according to Pitcher, CA is working on BrightStor SAN

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Designer's algorithms so that in the future, the product will be able to recommend various SAN components based on user goals such as performance or cost.

All three of these SAN design programs have pretty much the same objective--to save the user time by automating the tedious task of designing a SAN. The SAN design problem becomes progressively more complicated as more and more components are added into the SAN. The job of the SAN design tool is to make sure all the parts of the SAN work together, and then to optimize all the components of a SAN based on user goals, such as performance levels and cost restraints. To do so, for example, the user of HP SAN Designer selects a set of fabric nodes (switches and hubs), a set of links connecting pairs of nodes (hosts and devices), a topology with which to join these together and a single path through the network for each flow. The single-path restriction arises from SCSI request-ordering constraints.

Of course, the resulting fabric design must be feasible--that is, it must satisfy constraints that ensure it can be built, and it must support the connection and performance requirements. These constraints are: the number of links connected to a host, the device or fabric node must not exceed the number of ports available there (these restrictions are called degree constraints) and the flow routing must honor the bandwidth limitations of links and fabric nodes. And "it has become increasingly important to honor the interoperability constraints among vendors in designing heterogeneous SANs," says HP's Ward.

Obviously, no design tool is better than the inputs it is given. However, it's easy to build a certain amount of slack into the SAN design to allow for errors or anticipated future growth. Indeed, it's better to have the slack specified up front as part of the goal, rather than trying to build in slack after the fact by adding excess SAN elements in places where they may not do the most good, Ward says.

The HP SAN Designer algorithms run fast enough so that they can be used in interactive what-if scenario exploration, in conjunction with manual input from a SAN design expert. In most cases, it's important to use this tool--and other SAN design tools--in conjunction with a SAN design expert, so they can modify or further refine the output.

Ward says HP SAN Designer "is extremely valuable as part of an interactive SAN design process. It frees up the human SAN designer's time to explore interesting trade-offs between cost and other SAN features through multiple scenarios."

However, it's important to remember that most SAN design tools are in their first generation and don't offer all the bells and whistles to create the SAN of your dreams. But as they get better, designing a SAN will become much easier.

This was first published in July 2003

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