Warning: Copy a large amount of data

During complicated installation processes, it might be temporarly interesting, to take snapshots at important milestone points. But it is important to remove the snapshots when the configuration is terminated. Normally such tasks do not give any problems. But there are some exceptions in this kind of scenarios. Imagine you have fixed vhdx disks, that means that usually the diskspace consumption will not grow. But if you hadn't much diskspace left after creating the fixed virtual disks, you need to be very carefull. If you think to copy a large amount of data to a VM where you might have taken an initial snapshot (only during configuration time) it is important to know, that all your data won't be copied to the fixed vhdx disk, but rather to a avhdx file. So the data will be copied and your diskspace will decrease. When the physical disk is full, while the copy-process is still running, the VM will be saved. In such a scenario the VM will only be saved at the point, when you have approximately 30 MB of free space left on your phisical disk. The only way to go ahead is to immediately shut down your VM and to delete all snapshots. Depending on the amount of data which was already been copied, the main consuption of your important workingtime might just begin now: The merging-process is not just a simple copy-process. Even if you have only copied for example 150 GB of data (including large and little files), the merging time may take about 6 hours. If you wheren't able to delete any unused and large files on this disk before deleting the snapshots, the merge process runs at the low free physical disk space of about 30 MB.
This situation can become reality just if you have forgotten to delete the snapshots prior to copy large amounts of data to a virtual disk. For this reason Microsoft should think about a mechanism within Hyper-V to avoid such a troubleshouting process. It is a fact, that everyone can take snapshots with just one click, without knowing anything of how the command works.