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I expanded a disk for a VM in Hyper-V. Now I need to expand the volume but it has no contiguous space and it's a basic disk. Windows suggests to convert it to a dynamic disk but I heard that it might not be such a good idea to convert it to a dynamic disk.

Is it true that there is a risk in converting it to dynamic? And if so, how can I proceed? The volume needs urgent expanding.

Thanks for your help!

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  1. Backup the VM and make a checkpoint
  2. Convert the disk to dynamic https://www.thewindowsclub.com/convert-basic-disk-to-dynamic-disk-windows-8-7
  3. Extend the disk.
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Converting to a dynamic disc will probably not be a problem. What you are doing is a pretty simple operation. People run in to problem with dynamic disks in more complicated scenarios.

A better solution in the long term is to create only one volume per VHD. That way when you need to expand a drive in the future, you don't run in to this problem. To do that now you would need to shut down the VM and use third-party tools to copy the second volume out into its own VHD. You might run in to a problem here if you convert to a dynamic disk, since most of these utilities don't support dynamic disks.

A better immediate solution might be to enable dedupe on the volume, and kick off an optimization immediately. This might require a reboot (if dedupe is not already installed) but a quick reboot might be a good compromise between using a dynamic disk and not rebooting, and the extended downtime needed to implement "one volume per VHD". Plus you don't run the risk of not being able to implement "one volume per VHD" because you converted to a dynamic disk.

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If it's possible to create another small partition at the end of the disk (possibly by creating other small partitions to block and force the creation of your destination at the end, highest tracks) and move your existing volume there, then you can delete the prior partitions and create one larger contiguous partition.

If you have disk optimization software that won't trash your partitions it can be used on the last partition to gain the space to create a new temporary in the highest tracks to move to.

The other way is to simply buy a new disk and move it to there, once it's moved you can use your old disk as a secondary drive. Needless to say purchasing another identical drive has its uses too, if it's not a too out of date model.

It's a pancake flipping or Tower of Hanoi style problem.

  • Hi Rob, thanks for the help. I was not explaining it well, what I meant was that I have to now expand a volume on the disk inside the VM. So I have a disk in the VM with 2 volumes and 200 GB of free space. I want to expand the first volume which is not contiguous with the free space. Will it help to convert to a dynamic disk (and will it not have any bad consequences?) ? – Jozef Woo Sep 27 '18 at 15:01
  • Dynamic disks have been deprecated but there's no greater risk doing one type of low level operation versus another, creating a basic partition versus a dynamic one; you can lose it all either way. See: "What IS Dynamic Disk? How to Do Dynamic Disk Recovery?", "Change a dynamic disk back to a basic disk", etc. Using a DD will limit the tools available to manipulate the partition, but you can use one as a temp. – Rob Sep 27 '18 at 16:34

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