I have 4 1TB hard drives in RAID 1+0 configuration. Theoretically, I should have ~2TB of available space. Windows says the drive has a total size of 1.81 TB, which I'm fine with. As far as files on the volume go, I used WinDirStat to determine that I have 552.8GB of files on the volume. This means that I should have somewhere around 1.3TB minimum of free space. Yet Windows shows the drive as only having 492GB of free space. Are there hidden files somewhere that I can't see (I have show hidden files/folders turned on)? Does Windows not recognize that old files have been deleted? Is there any way to correct this problem?