Condusiv (the Diskeeper people) seem to make a compelling case for their Diskeeper 15 Server, saying that it is not a separate defrag utility but a frag preventer, and that people who say that defrag utilities should not be run on SANs / SSDs are correct but they are missing the point about excessive Windows I/O operations.
(I'm not pitching Diskeeper 15 because I haven't tried it, but I do have experience with and the highest respect for Diskeeper in earlier times.)
Is Fragmentation Robbing SAN Performance? (short blog post)
SAN Fragmentation Controversy Incites Attack from NetApp (short blog post)
3 Min Video on SAN Misconceptions Regarding Fragmentation (short blog post)
Can Windows hurt Flash Performance? (the 3-minute video)
Here is a excerpt from the third blog post (the highlighting is mine)...
Since the Windows OS takes a one-size-fits-all approach to all environments, the OS is not aware of file sizes. What that means is the OS does not look for the proper size allocation within the logical disk when writing or extending a file. It simply looks for the next available allocation. If the available address is not large enough, the OS splits the file and looks for the next available address, fills, and splits again until the whole file is written. The resulting problem in a SAN environment with flash or disk is that a dedicated I/O operation is required to process every piece of the file. In George’s example, it could take 25 I/O operations to process a file that could have otherwise been processed with a single I/O. We see customer examples of severe fragmentation where a single file has been fractured into thousands of pieces at the logical layer. It’s akin to pouring molasses on a SAN system.
Since a defragmentation process only deals with the problem after-the-fact and is not an option on a modern, production SAN without taking it offline, Condusiv developed its patented IntelliWrite® technology within both Diskeeper® and V-locity® that prevents I/Os from fracturing in the first place. IntelliWrite provides intelligence to the Windows OS to help it find the proper size allocation within the logical disk instead of the next available allocation. This enables files to be written (and read) in a more contiguous and sequential manner, so only minimum I/O is required of any workload from server to storage. This increases throughput on existing systems so organizations can get peak performance from the SSDs or mechanical disks they already have, and avoid overspending on expensive hardware to combat performance problems that can be so easily solved.
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