SOURCE: Bruce Boyers Marketing Services

April 14, 2010 16:49 ET

Defragmenting SANs: Now More Needed Than Ever

BURBANK, CA--(Marketwire - April 14, 2010) -  Sometime back, the term "storage area network" (SAN) was rarely heard outside of large enterprises. In recent years, however, vendors of SAN hardware and software have greatly simplified SAN installation, technical effort and maintenance, and reduced acquisition costs as well. This has made it possible for a much larger variety of businesses to take advantage of SAN technology.

Since file fragmentation is the most common cause of slow system performance, a crucial question becomes: is defrag necessary in a SAN environment?

That question is answered in the way that a SAN operates. In essence, a SAN is a replacement for a single disk, and replaces the disk driver with its own drivers. Any request to read or write data will have to go through these drivers -- but prior to that, any I/O request must go through the local disk file system. In Windows, of course, that file system is NTFS. When files are fragmented in NTFS, data is sent through to the SAN in a fragmented fashion, causing a great deal more I/O traffic. In the end, this causes the SAN to do more work than it should, and overall performance is affected.

The data originates within the NTFS file system. Data is also worked with on a day-to-day basis within NTFS. It therefore becomes obvious that for both the sake of the SAN and for the performance of production systems as well, defragmentation is crucial. When files are kept defragmented in NTFS, performance of all user systems is maximized. As well, far fewer I/Os are needed to write them to the SAN, and not only are transfer rates kept fast, but the SAN does not need to work as hard, helping conserve hardware resources.

Perhaps a reason for the sometimes conclusion that defrag is not needed in a SAN environment is that a SAN utilizes its own file system. But it must be noted that this file system does not defrag -- or in any other way affect -- NTFS. If files are fragmented in NTFS before being written to the SAN, the transfer times will be longer, period.

It is important to note that the type of technology used to defrag is important as well. In today's 24X7 computing environments, manual or scheduled defrag is usually inadequate, only because times to perform maintenance are rare to not occurring at all. Defrag must be fully automatic to be efficiently done.

A further note is that technology now exists to prevent a majority of fragmentation before it happens. This makes fragmentation a thing of the past, and allows SANs to attain the maximum performance required of them.

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