SOURCE: Bruce Boyers Marketing Services

August 04, 2009 14:10 ET

The Right Defrag on SANs Cuts Hardware Costs

BURBANK, CA--(Marketwire - August 4, 2009) - Storage Area Networks (SANs) are a significant development in storage technology. Not only do SANs remove storage traffic from production networks, as well as from server processing times, SAN technology also allows for real-time disk space allocation so that valuable drive space is not wasted. It is yet another major step for enterprises in the efficient utilization and maximizing of resources.

If not properly addressed, however, SAN resources can be wasted -- even with the use of thin provisioning. This is not due to any fault of the SAN processes themselves; it is due to the method with which files are saved and read by the Windows file system, below the level of thin provisioning, RAID or other solutions.

File fragmentation is a fact of life on all hard drives, no matter the storage methodology used. Left unchecked, fragmentation can cause files to exist in thousands or even tens of thousands of fragments, causing untold numbers of additional I/Os in reading and writing those files. This causes performance to slow dramatically and hardware life to be shortened considerably.

Thin provisioning, if used without fragmentation also being addressed, can not only result in slow performance but also wasted space. While the storage management system may allocate space using thin provisioning, the file system might 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. As new files are added, or data is added to an old file, or data is deleted, this difference between file system disk allocation and storage system thin provisioning can contribute to fragmentation, over-allocation, and less efficient use of storage space.

RAID can also be rendered less efficient by unchecked file fragmentation. When a file is saved, there are a number of attributes that must be checked which cost valuable system time. If an application has to issue multiple "unnecessary" I/O requests, as in the case of fragmentation, not only is the processor kept busier than needed, but once the I/O request has been issued, the RAID hardware/software must process it and determine to which physical member to direct the I/O request.

The solution to efficient SANs is efficient defrag that will work well in tandem with the technology. A fully automatic solution means that files and free space are always contiguous. Thin provisioning is therefore more efficient as deleted space is returned the SAN, thereby preventing over-allocation by the file system. RAID systems benefit from increased effectiveness as far fewer file attributes must be checked with each I/O request.

When implementing a SAN, ensure the correct defrag technology is also utilized to retain the utmost in SAN performance and reliability.

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