I was up late tonight working on some patching in a maintenance window when I saw the alert that a file server went below the 1 GB free mark. This is a secure file server using Windows BitLocker to encrypt the drive’s contents. I gave it more HDD space in vCenter then extended the volume in Windows Disk Management with 50GB of space. I knew that the next step was for BitLocker to automatically encrypt the new space I gave the drive.
I knew I should have around 50GB of free space now showing on the data drive in My Computer. But I only had 5.99GB available. What the #@%*??? What is causing Bitlocker to eat my free space? How is that possible? Refreshed a few times. Rescanned the disk a few times. Finally took my problems to Google (That’s happened a lot today…).
BitLocker apparently cannot ignore free space because it can contain remnants of old files. BitLocker creates a large placeholder file that chews up most of that fresh free space (44GB in my case) and then writes the crypto-bytes to the sectors where the temporary file was placed. If you need the free space immediately, you can pause encryption temporarily at the cmd line.
To get the full details, check out this TechNet article: Why does it appear that most of the free space in my drive is used when BitLocker is converting the drive?