Mark area as 'keep free'

Hello,

I'm a regular user of VMWare images, which can have large virtual HDDs, either fixed or flexible size. The issue I'm experiencing is that when I defragment, all files are neatly packed against eachother, for optimal positioning. In case of my flexible large virtual HDDs this means that at the first startup of my virtual HDD it becomes fragmented again, because the filesize of the virtual HDD is growing.

I cannot go for fixed size HDDs, because that would mean I have to reserve many GBs for empty space.

Is it possible to mark an area of the HDD in the userinterface as 'keep free' so that I have some extra space for growing my virtual HDD. What do you think?

I don't think the Windows API that defraggler uses supports this. I could be wrong, though.