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Performance penalty between dynamic- and fixed-size virtual hard disks?

Source: microsoft.public.virtualpc
Sent: 12/23/2008
From: VanguardLH <(email address - cut out)>
Message:

In some article of Microsoft's, it says a fixed-sized virtual hard disk
has better performance than a dynamically-sized virtual hard disk.
Okay, so how MUCH is the performance penalty if I use a
dynamically-sized virtual hard disk? VM's already run slower than the
host OS so the user already experiences a performance impact when
running software under the VM. That's the nature of the beast. I
haven't gotten into using Microsoft's free VM server on which I run
other guests because I don't have the hardware that could handle that
setup. So I'm using the software virtualization afforded by VirtualPC
for now.

If I create a 16GB dynamically-sized virtual hard disk, how much slower
will that guest operate regarding disk activity versus the same guest
using a fixed-size virtual hard disk? A lot? Very little? Just
noticeable?

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Related Messages

Re: Performance penalty between dynamic- and fixed-size virtual hard disks?

Sent: 12/23/2008
From: "Steve Jain [MVP]" <(email address - cut out)>
Message:

On Tue, 23 Dec 2008 18:10:11 -0600, VanguardLH <(email address - cut out)> wrote:

The only time you'll see a difference is when the dynamic disk is
writing to the hard drive and needs to expand the disk. Reads won't
make any real difference.

Personally, if you have a fast cpu and disk subsystem, you'll probably
not notice a difference. If you have multiple disks, moving the VM's
VHD off the primary OSes drive will probably yield a more noticable
differnce than running a fixed on the same disk.

--
Cheers,
Steve Jain, Virtual Machine MVP
http://vpc.essjae.com/

Show quoted text

>In some article of Microsoft's, it says a fixed-sized virtual hard disk
>has better performance than a dynamically-sized virtual hard disk.
>Okay, so how MUCH is the performance penalty if I use a
>dynamically-sized virtual hard disk? VM's already run slower than the
>host OS so the user already experiences a performance impact when
>running software under the VM. That's the nature of the beast. I
>haven't gotten into using Microsoft's free VM server on which I run
>other guests because I don't have the hardware that could handle that
>setup. So I'm using the software virtualization afforded by VirtualPC
>for now.
>
>If I create a 16GB dynamically-sized virtual hard disk, how much slower
>will that guest operate regarding disk activity versus the same guest
>using a fixed-size virtual hard disk? A lot? Very little? Just
>noticeable?

Re: Performance penalty between dynamic- and fixed-size virtual hard disks?

Sent: 12/23/2008
From: DevilsPGD <(email address - cut out)>
Message:

In message <(email address - cut out)> "Steve Jain
[MVP]" <(email address - cut out)> was claimed to have wrote:

Well, that isn't entirely true, odds are good that the expanded disk
will be heavily fragmented internally, so from a performance point of
view you're better off switching to a fixed disk.

Show quoted text

>Yeah, once your disks expand out fully, there would be no difference
>between performance, they'd both be "fixed" disks...with the option of
>your dyn-ex disk having the ability to be compressed in the future.

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