Virtual PC Virtual HDD under Windows XP....

[AtlantaBob]

I just installed Virtual PC on a Dell 700m that's running Windows XP Home. I had just defragged the disk and there was a large stretch of open space. Then I created a (fixed) 7 GB Virtual HDD (on a physical 40 GB HDD). When I went back to look with the defrag tool, Virtual PC had created a bunch of non-contiguous files, which windows considered to be fragmented.

I suppose that spreading the Virtual HDD over the disk could speed writes somehow... but it just seems more efficient to have placed it as a single large block. Any thoughts?

Edit: Now the Disk Defragmenting tool says that the fixed size HDD can't be defragged. What the heck?

 

[JeffreyLebowski]

Is the virtual hard disk, static, or Dynamic. I never checked defrag, but I would think if it was dynamic it would just use contiguous for the part that has data and expand it when needed.

 

[RebateMonger]

Microsoft's Stephen Cracknell blogs on tuning Virtual PC for best performance. Part 1

Part 2

 

[stash]

I wonder if he realizes he has a link to the MS intranet on there.

 

[AtlantaBob]

Originally posted by: RebateMonger
Microsoft's Stephen Cracknell blogs on tuning Virtual PC for best performance. Part 1

Part 2

I came across those last night (admittedly after posting this), but I'm still a little interested in why Virtual PC would create a non-contiguous static hard disk. Surely this isn't something for Highly Technical 🙂

Jeffrey, it is indeed, static, and I'd tend to agree with what you said re: the dynamic disk...

Edit: And, duh, thanks for going to the trouble of finding those links! (It's been a long time since i had my morning coffee.)

 

[spyordie007]

but I'm still a little interested in why Virtual PC would create a non-contiguous static hard disk.

Not sure exactly what you're after here, can you elaborate?

If you're using dynamically expanding VHDs than they arent going to be contiguous on the host as the size increases over time. On way to increase performance and minimize this problem is to allocate the space to a fixed size VHD (so the only defragging you would have to do is from within VPC).

Erik

 

[AtlantaBob]

Originally posted by: spyordie007

but I'm still a little interested in why Virtual PC would create a non-contiguous static hard disk.

Not sure exactly what you're after here, can you elaborate?

If you're using dynamically expanding VHDs than they arent going to be contiguous on the host as the size increases over time. On way to increase performance and minimize this problem is to allocate the space to a fixed size VHD (so the only defragging you would have to do is from within VPC).

Erik

Erik,

Sorry for the confusion. I specifically created it as a fixed-size (non-dynamic) hard disk. Like you, I imagined that a fixed size hard disk would obviously be a contiguous block, so all defragmentting issues would be within the guest OS itself. Anyway, it turns out that in my case, the fixed-size Virtual HDD was scattered all over the place (And I didn't have any blad clusters or other fragmented files to blame it on... the defrag tool specifically showed a huge blank area of disk right before I created the fixed size HDD).

 

[spyordie007]

I see what you're after. I dont know that VPC looks for contiguous space before allocating for the VHDs so it may just grab the next free sectors on the drive.

Can you simply shut down the guest OS and than defrag from within the host OS? Since the VHD is fixed size you should only have to do this once.

 

[AtlantaBob]

Yeah, apparently that's what it does... I was planning on doing that, but as it turns out, 7GB in a single file is too large for the Windows defragger to handle. One of the above links suggests that you zip the .vdd (?) Virtual HDD file and then defrag, but, you guessed it, it's too big for the compression program too! There seem to be some other possibilities, but I just got a new laptop at work today, so perhaps I'll just turn this one into a full-blown Linux machine.

 

[kobymu]

There is the old tactic of: defrag, copy the file to the same partition, check if the new file is now in a single block on the partition, if not repeat until the newer file is a single block (copy1, copy2 , copy3 and so on). Once the desired affect has been accomplished, then all the old copies can be deleted and the single block file should be rename back to the original file name.

 

[Robor]

Originally posted by: stash
I wonder if he realizes he has a link to the MS intranet on there.

What's the point of that? Only kenfrost2001 can get to it because unlike everyone else he's running on the intranet. Sorry, I had to say it! 😛 😉

 

[Nothinman]

Then I created a (fixed) 7 GB Virtual HDD (on a physical 40 GB HDD). When I went back to look with the defrag tool, Virtual PC had created a bunch of non-contiguous files, which windows considered to be fragmented.

Then blame Windows, VPC just says "create me a 7G file" and the Windows block layer and NTFS driver decide where on disk to place all of the blocks.