Why do my VirtualBox VMs take more space than they should?

Question

I have VirtualBox with 91 virtual machines, each virtual machine has a static hard disk with 20 GB.

I have Ubuntu, Windows, Mac OS X operating systems, each of them takes no more than 5 GB. I also installed a few programs that don't take more than 1 GB.

So each virtual machine has 14 GB of free space. In "statistics" however, I see that every hard disk of the virtual machines takes 20 GB.

Therefore I use 1820 GB, but it should be less than 600 GB. Why is it over 1 TB?

Answer 1

If I understood you correctly, you've created fixed size virtual hard disks.

If you create fixed size hard disk, then it is preallocated, so your virtual hard disk file will be always 20 GB, disregarding whether all of it or only 5 GB are actually used. Consider creating dynamically expanding hard disk instead. Then your virtual hard disk files will grow as they need.

Fixed size hard disk have slightly better performance though.

The other reasons for additional space taken might be snapshots / saving state instead of powering off VMs (not that order of magnitude in case of state-saving - it's something like RAM dump - but in case of many snapshots, this can happen).

You can not generally change fixed disk to dynamic in place, you have to create new dynamic disk and then clone contents from your old fixed disk to new dynamic one.