This one is easy to overlook and can have you scratching your head weeks to months later. Recently disk space has been mysteriously disappearing on a few select servers of mine. The free/used ratio was way out of whack with >75% of the disk being reported as used by Windows on certain drives. Auditing the drive reveals no culprit, with all visible files not consuming anything near what is being reported, including hidden files. System Volume Information reports 0 bytes and access is denied to this folder. If you use Windows Server Backup (WSB), in Server 2008 R2, and in particular VSS backups this can happen to you too (or VSS at all for that matter).

WSB uses VSS for backups and you have two choices in your backup sets: VSS full or copy backups.

 

In either case the backup job will create a Shadow Copy task on the volume pertaining to your backup. By default the shadow copy task is set to use no limit which will, eventually, completely consume your drive. The tricky part is that the space consumed by VSS is not visible in Windows Explorer and if you don’t set a hard limit on the shadow copy it can grow out of control.

Make sure to limit these and you should be ok. Changing no limit to use limit will immediately delete and free space on your server!

VSS settings are accessed by opening the properties of any drive in your server and selecting the Shadow Copies tab.