Method 1:

EXEC MASTER..xp_fixeddrives

GO

Method 2:

SELECT DISTINCT DB_NAME(dovs.database_id) DBName,

mf.physical_name PhysicalFileLocation,

dovs.logical_volume_name AS LogicalName,

dovs.volume_mount_point AS Drive,

CONVERT(INT,dovs.available_bytes/1048576.0) AS FreeSpaceInMB

FROM sys.master_files mf

CROSS APPLY sys.dm_os_volume_stats(mf.database_id, mf.FILE_ID) dovs

ORDER BY FreeSpaceInMB ASC

GO

引自：SQL SERVER – Disk Space Monitoring – Detecting Low Disk Space on Server