SAN Realizes Its Potential with Proactive Defrag

Some things are good ideas from the start, and one of them is the Storage Area Network (SAN). It has great success potential, especially potential for delivering on the promise that storage not directly attached to the server will bring advantages in provisioning and performance, reliability and availability.

But these very real advantages don’t eliminate the need for IT maintenance actions to permit the best possible SAN performance and reliability.

“One of the most significant potential issues, and probably the most unrecognized, is defragmentation in a SAN storage system. With the implementation of a SAN in their storage environment, many Windows Server administrators believe that defragmentation, which they accepted and dealt with when using DASD storage, has gone away.” This statement, made by David Chernicoff of Windows IT Pro in his paper, “Maximize the Performance of Your Windows SAN Infrastructure,” points out a basic misstep that can be costly to IT administrators.

A SAN is agnostic when it comes to server operating systems. And the SAN appears to the operating system as locally attached storage. It is inherent in SAN storage that the operating system isn’t aware of the type of storage it uses and can’t optimize for a particular storage model.

This also means that SANs are not built to prevent or correct fragmentation. When you store information in your SAN, fragmentation at the file system level creates operating system overhead that interferes with file retrieval. These events are not caused by the SAN, and it’s outside the scope of your SAN to do anything about them.

Storage administrators can fail to consider this when they run into reduced efficiency. When they notice performance problems, many administrators add additional storage, assuming that a lack of free space is causing slowdowns. They fail to consider that both performance and reliability are often affected by the fragmentation that occurs when Windows Server writes data to any storage ― and that’s not just DASD or NAS, but also SAN.

This fragmentation often shows up as reduced application performance. Application response time begins to increase, it takes longer to load files, and applications loaded from the storage take longer to launch. Your IT team can receive help desk calls with complaints about a variety of supposed problems, when the real problem is that fragmentation is causing data manipulation times to increase to the point where the delays affect the user.

Since it isn’t a SAN function to manage fragmentation, it’s important to address the fragmentation at its source. Of course, the ideal solution to this phenomenon would be to prevent it. That would mean writing to the SAN using technology that minimizes fragmentation as the data writes, so your system would be passing fewer, larger disk I/Os to the SAN. You would thus reduce operating overhead and raise your I/O efficiency.

Defrag has been automated for years by Diskeeper Corporation defrag applications for systems ranging from individual workstations to enterprise servers. Today Diskeeper® 2010 with IntelliWrite® technology takes defrag a step further by preventing fragmentation from happening in the first place. Its proactive defrag is much easier on the budget than throwing storage expansion dollars at your SAN performance issues.