Assuming a XP SP2 Guest, configured using a sparse virtual hdd, does it makes sense to defragment the virtual disk, from inside XP guest itself, using the XP defragmentation tool?
I tried this yesterday, doesn't seem to make much of a difference, although the WinXP hard drive looked very fragmented before running the utility. Any advice from programmers?
Defragmentation will not effect speed of execution (at least at the way it will be noticable). And will not even change the size of your hdd image. Basically, if you want to decrease size of your hdd you should use separate tools (Compactor, etc.). But you will not affect performance anyway - cause disk usage is a very rare event as the result of large disk caches in most modern OS.
I'm not entirely sure I would agree with this statement, though I don't have any information on the internal file format of the PW HDD hard disk files. Defragging is of course an attempt to minimize seek overhead by making file data contiguous. In a VM, you need to defragment at THREE levels for it to be effective: (a) You need to defrag within the guest OS so that the files are "logically" contiguous as far as the guest OS knows. They are then arranged on logically contiguous blocks within the virtual HDD. (b) You need to defrag within the VM host (Parallels Workstation), assuming that the HDD format allows some form of logical -> physical mapping. THis will re-order the virtual physical blocks in the HDD image so that they are contiguous. At this stage, the file system is logically continuous within the virtual HDD file. (c) Finally, you really need to defrag on the host OS (Mac OS X) so that the HDD file is itself physically contiguous on the underlying hardware. If you can do all three steps, it *might* make a small difference, but I wouldn't bother too much myself. At some future time, PW have talked about supported physical partitions in PW (like VMware). In this case, de-frag in the guest OS will indeed make a difference.
