Published: 14 Jul 2003
Designing a large storage area network (SAN) fabric is a complex job. Overprovisioning a SAN will run up the costs substantially, and an underperforming SAN can be equally costly. SAN design tools from Computer Associates, EMC, Hewlett-Packard and other companies are starting to appear, and these products can take some of the guesswork out of constructing a well-tuned SAN.
"As users move to heterogeneous, fabric-attached storage environments, the complexity of managing the increasingly diverse number of devices and the associated levels of software versions increases the effort required to define a solid design and to test the impact of any change," says Carolyn DiCenzo, research VP of storage management software, at Gartner Inc. "There is clearly a need for software to automate this effort, supporting the design and reducing the risk as changes are made to the environment."
|What to look for in a SAN design tool|
To help design its internal SANs, Hewlett-Packard (HP) developed a set of tools collectively called "Appia, after the Appian Way, one of the networks of roads leading to ancient Rome," says Julie Ward, project scientist at the decision technologies department, HP laboratories, in Palo Alto, CA. HP recently renamed Appia, and it is now called HP SAN Designer.
HP SAN Designer can design Fibre Channel (FC) SANs and in the "near future," Ethernet SANs, an HP spokesperson says. It works with a variety of storage products, not just HP gear. Ward claims that HP SAN Designer can reduce the cost of a SAN by a factor of three over a manual design.
"But even more important than the cost savings is that the designs can be built--they honor the physical constraints of the system and produce the desired degree of reliability. It is very difficult to verify correctness when designing a large-scale SAN manually," Ward says.
Even if a manually designed SAN works, it may not work optimally if the fault-tolerance aspects are not fine tuned. And in many cases, it's difficult to grow a poorly designed SAN to include hundreds--or even thousands--of storage devices.
HP SAN Designer's algorithms and similar SAN design tools balance SAN criteria such as work loads, device performance, protection levels, disaster tolerance and overall performance demands to configure the storage fabric. HP SAN Designer can analyze data flows at a granular level. From each host to each storage device, it suggests the preferred data paths and load balancing. In addition, HP SAN Designer can automatically modify the SAN as it grows and evolves, according to Thomas Goepel, HP's portfolio manager for storage services.
HP SAN Designer isn't sold or licensed. "The use of the tool is part of the standard HP SAN design delivery," says Goepel, adding, that in the future, the tool will be "more tightly integrated into HP's sales tools."
EMC is also jumping on the SAN design tool bandwagon with SAN Architect, a new Web-based software program for SAN design, modeling and validation. The template-driven SAN Architect is particularly suited for customers with rapidly changing SAN environments, planned multiple server, switch or array rollouts and consolidations and even those who simply need to validate changes or implementation plans without interrupting production systems.
SAN Architect guides storage architects and IT administrators through the design and validation of a fully functional SAN. It ensures that proposed changes are accurate and precise by modeling and validating hosts, host bus adapters (HBAs), switches and storage arrays, producing a final design that's 100% supported by EMC.
According to Randy Carter, a SAN architect at Radian Group Inc., in Philadelphia: "Before SAN Architect, SAN design involved consulting numerous compatibility reference sources, manually white boarding out the flows, building a Visio presentation and, finally, creating an Excel spreadsheet to fit everything together. What used to take 24 hours now takes four."
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 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.