Does fragmentation affect SANs, NAS and RAID? Most people believe not. Yet a recent paper released by Diskeeper says otherwise. In fact, the company says that disk arrays are just as prone to fragmentation as a single physical drive would be.

These devices do suffer from fragmentation. This is attributed to the impact of fragmentation on "logical" allocation of files and to varying degree, their "physical" distribution. The file system driver, NTFS.sys, handles the logical location (what the operating system, and a defragmenter affect). The actual 'writing' is then passed to the fault tolerant device driver (hardware or software RAID), which then, according to its procedures, handles the placement of files, and generating parity information, finally passing the data to the disk device driver (provided by drive manufacturer).

The paper by Diskeeper may be downloaded here.