Stripe and Mirror Set Defragmentation
Diskeeper is compatible with hardware and software RAID. It treats hardware RAID devices the same as common stripe sets and mirror (or shadow) sets.
Physical members in the RAID environment are not read or written to directly. The Windows NT file system sees it as a single "virtual" drive. This virtual drive has logical cluster numbering just like any other partition supported under Windows NT.
As an application reads and writes to this virtual environment (creating new files, extending existing ones, and deleting others) the free space becomes fragmented, thus causing new and existing files to be fragmented as they are written. Because of this fact, fragmentation on this virtual drive WILL HAVE a substantial negative performance effect. When an I/O request is processed by the file system, there are a number of attributes that must be checked which cost valuable system time.
Diskeeper sees the RAID environment just as the file system does. That is, Diskeeper defragments the virtual drive. Diskeeper improves the speed and performance of a RAID environment by eliminating these wasteful and unnecessary I/Os from being issued by the file system. This occurs because the file system sees the files and free space as being more contiguous.
The file system will spend less time checking file attributes which means more processor time can be dedicated to doing real useful work for the user/application. In addition, these I/O requests are now much more likely to fill the entire 64K chunk size with the I/O now taking full advantage of the RAID.
Mirror sets are handled in much the same way as stripe sets, with each copy of the mirrored file being defragmented separately.
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