Windows – Cannot convert basic disk to dynamic disk. Not enough space

Since you still have all your data on the span with disk 2 and 3, you can:

1. Create a new BASIC disk (disk4)
2. Copy all data from the span to the basic disk 4.
3. Shutdown the VM
4. Remove disks 2 and 3.
5. Remove disk 4 (remove from VM, remove, not delete!)
6. Add the disk file back as disk 2

How to do this precisely depends on your software. VMware? Qemu, virtual PC, ... ...

And as always, make a backup before you do this. Better safe than sorry.

An alternative is to copy the VM.

• Create a new VM with two basic disks.
• Copy the disk file for from the working install (OS disk only!)
• Use the network to copy files from the other VM to this one.

Effectively you do the same, but you keep the old VM around rather than making a backup.
If you do this you might want to double check how your VM software allocates MAC addresses and you might get a duplicate name on network problem. (The latter is a guess. I know Xp and win7 will throw that, but I never needed to do this with server 2008).

I believe I have heard it said that at least 1 MB of unallocated space is required at the end of the disk to create the database for the dynamic disk.

When Windows creates the partition it does this automatically, and this unallocated space is not shown in Disk Management with Windows 7. Win2K and early versions of XP will show this space, typically 7-8 MB. I think MS decided to hide it so people would stop asking why that space couldn't be included in a partition.

If you created or resized the partitions using a 3rd party tool, this space may have been allocated, which will prevent converting to Dynamic.

My advice is therefore to shrink the partition so as to leave at least 100 MB of free space at the end of the disk.

If this doesn't work, one of the usual workarounds is to delete all partitions, reinstall a vanilla Windows 7 without activation and then restore the image, since the newly created partition will be correctly allocated. Partition sizes are less important, since (if I am not wrong) Acronis can restore an image to a different-sized disk.

The MS article Dynamic Disks states :

Dynamic disks offer greater flexibility for volume management because they use a database to track information about dynamic volumes on the disk and about other dynamic disks in the computer. Because each dynamic disk in a computer stores a replica of the dynamic disk database, for example, a corrupted dynamic disk database can repair one dynamic disk by using the database on another dynamic disk. The location of the database is determined by the partition style of the disk. On MBR partitions, the database is contained in the last 1 megabyte (MB) of the disk. On GPT partitions, the database is contained in a 1-MB reserved (hidden) partition.