11 Replies Latest reply: Dec 5, 2012 8:06 PM by ds store
R. Toby Richards Level 1 (0 points)

Yes, I have read the official Apple Support document about why I don't need to defragment my Mac (http://support.apple.com/kb/HT1375). I've also read many third party articles about this. I get it, yet I think I may have a case for an exception:


I work with lots of virtual machines. Now, unless I want to waste time pre-allocating disk space then I have to use dynamically sized disks of 32 or more GB. One of the things that HT1375 says is this:


Fragmentation was often caused by continually appending data to existing files, especially with resource forks. With faster hard drives and better caching, as well as the new application packaging format, many applications simply rewrite the entire file each time. Mac OS X 10.3 Panther can also automatically defragment such slow-growing files. This process is sometimes known as "Hot-File-Adaptive-Clustering."


First of all, I have read that "Hot-File-Adaptive-Clustering" went away in 10.6. Secondly, "simply [rewriting] the entire file each time" isn't going to be a viable option for files that are dozens of GB in size. I also understand that OSX compensates for fragmentation in other ways, such as "read-ahead and write-behind caching". The problem is that the virtual OS does not. I can defragment its virtual hard drive, but that dosn't do a lot of good when the file that *is* the virtual hard drive itself is fragmented.


So let's have it: are there exceptions to the standard answer to defragging a Mac? If so, then can it be done without great difficulty?

MacBook Pro, OS X Mountain Lion (10.8.2)