A recent article by Computing Technology Review's Tom Joyce discusses the fact that every major advancement in enterprise computing comes with a new set of performance management challenges. This is certainly true of RAID technology--even though some argue that RAID is a performance solution and doesn't need defragmentation. However, tests and testimonials have proven otherwise.
RAID (Redundant Array of Independent Disks) creates a virtual volume, made up of multiple disks. Data written to the RAID set is written redundantly so if one disk should fail, all of the data is still available, many times with no visible interference to the user. This means greatly reduced or no downtime for vital applications such as databases. The operating system "sees" the RAID set as one volume; data is written physically to the disks through the RAID controller which also creates a copy of each data block.
RAID technologies also improve performance; since the I/O load is across several disks retrieval is faster. But the myth that fragmentation does not affect RAID arrays is truly a myth. As an application reads and writes to this virtual environment (creating, editing and deleting files) the files become fragmented. Fragmentation on this logical drive will negatively affect performance. When an I/O request is processed by the file system, there are many attributes that must be checked, taking valuable time. If an application has to issue multiple "unnecessary" I/O requests, as in the case of fragmentation, the processor is kept very busy and the RAID hardware/software must process it and determine which physical member to direct the I/O request.
A defragmenter sees the RAID environment just as the file system does. Therefore it defragments the logical drive, improving the speed and performance of a RAID environment by eliminating unnecessary I/Os from being issued by the file system. This occurs because the file system sees the files and free space as contiguous. Now the system spends less time checking file attributes freeing processor time for conducting useful work.
With today's enormous disk capacities, file sizes, and higher-than-ever access demand on RAID sets through servers, enterprises must pay attention to file fragmentation and defragmentation technology. The true solution in high-demand server environments is a third-party defragmenter, such as Diskeeper 2008 which requires no scheduling and has the ability to defrag in real-time to keep pace with today's frantic fragmentation rates.
On the onset, fragmentation seems like a minor issue, but those who are frustrated with the stability issue of busy servers and their performance deterioration will beg to differ. Even with the large high speed drives, its effect on performance and productivty cant be overlooked. This is one malady thats best prevented than cured at the serious stages.
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