Disk I/O - bootcamp vs. non-bootcamp

S

slimemold

Hunter
I recently decided to do away with bootcamping my XP, and went with a virtual disk for my WinXP. Running 4128 (and now the latest that was released today), no difference.

But basically, it seemed to me that disk accesses under bootcamp were a lot faster than with a virtual disk.

Also, I noticed that my Inactive memory skyrocketed after moving to a virtual disk. Under bootcamp, with the apps I run, I almost never need to do any page-outs, and inactive memory was bounded reasonably. But with the virtual disk, it's constantly paging out, and inactive memory constantly fills up the rest (as in, I have no free memory left).

I've got a Macbook Pro (previous generation, not the new Santa Rosas) with 3GB RAM. Allocated 1GB to WinXP.

Anyone else have any anecdotal evidence that I'm not going crazy?

I wonder if there are two levels of paging going on with a virtual disk...what WinXP is doing in its filesystem cache, and what OSX is doing in its filesystem cache. Is parallels not doing writes with immediate commits to media? Might that have something to do with the huge amounts of memory being used?
 
Well, yeah. When I had WinXP under bootcamp, my disk was indeed partitioned with bootcamp. Now, with WinXP under a virtual disk, the bootcamp partition was removed prior to the WinXP reinstall onto the virtual disk.

What was the point of your comment?
 
Probably because partition cannot get fragmented, but virtual disk file can be fragmented all over hard drive.

Radek
 
That's a reasonable guess. Alright, I'm going to use iDefrag to do a full defrag and compaction, to rule this out. Stay tuned.
 
Okay, I've defragmented my virtual disk (actually, I defragmented/compacted my whole OSX drive using iDefrag). I still notice that disk I/Os are slower than when I was using bootcamp.
 
A virtual hard drive will always be slower than a non-virtual hard drive such as with BootCamp. This is the case with VMware (on both Macs and PCs) as well.

If you think about it, it should make sense. A virtual hard drive is a file that has to grow as you add files to it from Windows. This is bound to be slower than a physical partition such as Boot Camp, which does not have to do this.

I have found that a fixed-size virtual disk is closer in speed to a physical disk, but still not as fast, because it is a just a file after all and does incur some overhead because of that.
 
slimemold said:
I've got a Macbook Pro (previous generation, not the new Santa Rosas) with 3GB RAM. Allocated 1GB to WinXP.
Click to expand...

You are more knowledgeable than I am, but have you tried allocating only 512 MB to XP?

David
 
Yes, I realize that a virtual disk will always be slower than a real, physical disk, due to the extra layers it has to go through. I'm mostly wondering why disk accesses seem to be cached on the OSX filesystem level. Doing this creates two levels of disk block caching - one in OSX, and another in the virtual machine, leading to redundant information and a waste of memory.

And yes, I've tried only allocating 512 MB to XP. I mainly use Visual Studio 2005 in WinXP, and 512 is not enough for that...I get constant disk thrashing.
 
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