Consider SQL Server databases being backed up to a shared drive, mounted volume or disk drive for another server with no sql server data and/or log files.
Capacity Manager will only give you information for a disk on which SQL Server data and/or log file is stored. The Disks Information bar chart displays the distribution of target server disk space used for consolidated data and transaction log files, and the amount of unused disk space available to the target on each disk drive. It therefore means that, except your system and user databases for a SQL Server resides on that disk, it won't give you information for the disk.
More over, information on free space is based on database and log files present on disk. Each drive that stores instance information is represented by three bars showing the space used for transaction log files, data files, and free space. Drives that do not contain data or transaction log files for the instance will not appear on chart. The vertical axis shows the disk space size and unit of measure. The horizontal axis shows each disk drive.
The legend displays the colours that represent the log file, data file, and unused space in the chart.
