If the disk is already in exclusive use by another program or is formatted using a file system other than NTFS file system, FAT, or FAT32, it can't be defragmented.
Network locations can't be defragmented.
If a disk that you're expecting to see under Current status is not showing up there, it might be because it contains an error. Try to repair the disk first, then return to Disk Defragmenter to try again.
Article ID: 17126 - Last Review: May 12, 2016 - Revision: 15