Q: Why is my virtual machine not big enough for Windows 10?

Q. I created a virtual machine to run Windows 10 and the new Office Preview. It’s worked fine through several iterations of both Win 10 and Office — until today. I started getting unhelpful messages that the hard drive isn’t big enough.

I attempted to resize the drive using the VBoxManage command, but I ended up with two partitions. I’ve tried the disk management tool, but nothing lets me extend the C: drive to combine the two.

I might have solved my problem temporarily by using Windows’ Disk Cleanup and deleting everything I could think of. But now Win 10 is trying to update. What happened? And how can I keep it from happening again?

A. Each new Win10 Preview is essentially a complete new version of the OS. Consequently, the downloads and installs take up a ton of disk space — far more than a single, stable setup. VirtualBox’s dynamic disks start small but then grow to the maximum size you set when you initially created the disk. A 25GB disk, for example, will start out using only as much space as the installed VPC needs; but it will grow to a max of 25GB. It can’t get larger than that. So, you simply ran into a drive-size ceiling.

I suggest deleting your current Win10 VPC entirely. Update VirtualBox (including the extension packs) and then download and install the current Win10 build afresh. Chances are, it’ll work fine — at least until Win10 changes yet again.

Once Win10 formally ships, and VirtualBox and/or its extensions are updated to accommodate the as-shipped OS, things should settle down.

(Originally published on Windows Secrets on Thursday, June 18, 2015.)

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