SOURCE: Bruce Boyers Marketing Services

May 18, 2010 14:14 ET

Prevent Fragmentation on SANs and Cut Hardware Costs

BURBANK, CA--(Marketwire - May 18, 2010) -  Storage Area Networks (SANs) have long since removed storage traffic from production networks and eased server processing times. They are now available to many companies that before could not have afforded to implement this technology, thanks to simplification of hardware, software and installation. Technology (as it always does) has continued to improve, with drives continuing to become faster and more efficient, and new technologies such as virtualization now being incorporated to make SANs even more efficient.

SAN technology is certainly advanced. But despite all of its enhancements, if one crucial and basic problem is not addressed, it will critically impact the SAN performance on which the enterprise is counting. This is not through any fault in SAN processes; it is due to the fact that files are saved and read to drives by the Windows file system, below the level of SAN's many enhancements.

A SAN still relies on hard drives, and unfortunately file fragmentation is a fact of life on hard drives. File fragmentation causes files to exist in thousands or even tens of thousands of fragments, causing highly excessive additional I/Os in accessing those files. Performance is dramatically slowed and hardware life is considerably shortened.

One great advancement to SAN technology is thin provisioning. But thin provisioning, if used without fragmentation also being addressed, not only loses performance but also wastes space.
The storage management system allocates space using thin provisioning, but the file system may simply write data wherever it finds space. If data is written to a "high" logical cluster number (say, cluster 200), all clusters from zero to 200 are then allocated even if they are not used. When data is added to an old file, new files are added or deleted, or an old file is expanded, the difference between file system disk allocation and storage system thin provisioning can contribute to fragmentation, over-allocation, and less efficient use of storage space.

Another major component of SAN technology, RAID, is also affected by fragmentation. As a file is saved, a number of attributes must be checked for that file, costing valuable system time. In the case of a fragmented file, there are multiple additional I/O requests. 

Virtualization is also greatly impacted by fragmentation. A virtual machine has its own I/O request which is relayed to the host system, so multiple I/O requests are occurring for each file. When files are fragmented, the generation of multiple I/O requests occurs for each fragment of every file. This action is multiplied by the number of virtual machines resident on any host server.

The most efficient way to keep a SAN running at peak performance and reliability is with a fully automatic solution to deal with fragmentation. With the technology available today, a majority of fragmentation can actually be prevented -- an ideal solution for all SAN systems.

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