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VHD - Dynamic vs fixed considerations

I have a drive I imported to a VHD that was originally 250 gig with only 170 gig of actual data  but I had to convert it to Dynamic as there was not enough space on the physical drive hosting the VHD along with other VHD's. When I converted it to Dynamic it shrunk the drive to 170 gig.  What I then tried to do was convert it to a fixed VHD of 200 gig but when I went to convert it to Fixed it wanted to go back to 250 gig - the original physical size of the drive. Here are my questions:

Is there any way I can convert a Dynamic drive to a specific Fixed size? If not with native tools that come with 2008 then other Microsoft or third party utilities?

Is there any way I can set the minimum size for a Dynamic VHD. What I want to do is to start with a dynamic size about 20 gig more than the current data area that will be on the VHD so that it would be quite a while before the VHD would need to 'expand' dynamically?

My VHD's are on a physical  drive that is software mirrored via the innate software mirroring capabilities of Windows 2008.  Is there any complication from the fact that the VHD's housed on the physical drive are dynamic as opposed to fixed?

What if any hit is there on performance with system drive and data drives with Dynamic VHD's? What circumstances would there be where I would want to us one versus the other?

What implications are there for Windows Server Backup as far as Dynamic VHD's go if I ever have to do a bare metal recovery as opposed to having had fixed VHDs?

Will there be any problems with Dynamic VHD's if I try to Ghost them? Ghost converts Dynamic mirrored drives to Basic - what will it  do with Dynamic VHD's?

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lineonecorp
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lineonecorp
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gtworekCommented:
> Is there any way I can convert a Dynamic drive to a specific Fixed size? If not with native tools that come with 2008 then other Microsoft or third party utilities?

No. You can create Fixed disk and then copy your data using any disk copying software.

> Is there any way I can set the minimum size for a Dynamic VHD. What I want to do is to start with a dynamic size about 20 gig more than the current data area that will be on the VHD so that it would be quite a while before the VHD would need to 'expand' dynamically?

No. Fresh VHD has no data at all. If it's dynamic it has only BAT area and of course starting and ending data structures. Look at http://technet.microsoft.com/en-us/virtualserver/bb676673.aspx for detailed specs.

> My VHD's are on a physical  drive that is software mirrored via the innate software mirroring capabilities of Windows 2008.  Is there any complication from the fact that the VHD's housed on the physical drive are dynamic as opposed to fixed?

No. It emulates physical drive pretty well and it is not important is fixed or dynamic. Of course you should remember about some performance loss in dynamic disks.

> What if any hit is there on performance with system drive and data drives with Dynamic VHD's? What circumstances would there be where I would want to us one versus the other?

Dynamic VHDs are really slow during some write operations. In read they works pretty well. Look i.e. at http://blogs.technet.com/winserverperformance/archive/2008/09/19/hyper-v-and-vhd-performance-dynamic-vs-fixed.aspx 

> What implications are there for Windows Server Backup as far as Dynamic VHD's go if I ever have to do a bare metal recovery as opposed to having had fixed VHDs?

They decided to dynamic ones beause they take less space - equal to space occupied by data not to entire volume.

> Will there be any problems with Dynamic VHD's if I try to Ghost them? Ghost converts Dynamic mirrored drives to Basic - what will it  do with Dynamic VHD's?

Ghos will not "see" if your VHD is fixed or dynamic. Will work exactly same way.
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lineonecorpAuthor Commented:
Thanks for taking the time to provide all the responses/links - very informative.  

A couple of clarifications.

+++++++++

> Is there any way I can convert a Dynamic drive to a specific Fixed size? If not with native tools that come with 2008 then other Microsoft or third party utilities?

>No. You can create Fixed disk and then copy your data using any disk copying software.

So if I have a Dynamic VHD that's 200 gig I can simply create a fixed VHD let's say of 225 gig and copy the Dynamic one to it even using just the built-in copy/paste command and I will have 25 gig to spare?

+++++++++
> Is there any way I can set the minimum size for a Dynamic VHD. What I want to do is to start with a dynamic size about 20 gig more than the current data area that will be on the VHD so that it would be quite a while before the VHD would need to 'expand' dynamically?

>No. Fresh VHD has no data at all. If it's dynamic it has only BAT area and of course starting and ending data structures. Look at http://technet.microsoft.com/en-us/virtualserver/bb676673.aspx for detailed specs.

Let's say it's an 'occupied' VHD - it already has data on it.  Can I increase the size manually then? Can I set rules on how much space it can take at a time? Set up a warning that it's running out at let's say X amount below max capacity?


+++++++++

> What implications are there for Windows Server Backup as far as Dynamic VHD's go if I ever have to do a bare metal recovery as opposed to having had fixed VHDs?

>They decided to dynamic ones beause they take less space - equal to space occupied by data not to entire volume.

So no impact - I can bare metal recover a backup that was done from a Dynamic VHD no different than from a fixed VHD?
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gtworekCommented:
> So if I have a Dynamic VHD that's 200 gig I can simply create a fixed VHD let's say of 225 gig and copy the Dynamic one to it even using just the built-in copy/paste command and I will have 25 gig to spare?

It depends on the amount of data on dynamic disk. If you make dynamic disk growing to 200GB, then you delete 100GB - your VHD still has 200GB and there's only 100GB of data. If you copy it to 225GB fixed disk - you have 125GB free.

> Let's say it's an 'occupied' VHD - it already has data on it.  Can I increase the size manually then? Can I set rules on how much space it can take at a time? Set up a warning that it's running out at let's say X amount below max capacity?

You cannot increase the size manually. But you can create large file (with 'fsutil file createnew' command) and then delete it. Your VHD will expand but will not shrink after deletion. Does it solve your problem? There's no warnings about VHD capacity except "normal" system warnings about full volumes.

> So no impact - I can bare metal recover a backup that was done from a Dynamic VHD no different than from a fixed VHD?

Sure. If you mount VHD it the data on it behaves same way and this doesn't depend on VHD type. It's just a disk and you can even see it in your device manager.
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lineonecorpAuthor Commented:
Great. I especially like the trick about creating a large file and then deleting it so I end up with  a large Dynamic VHD with room to spare.
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