although generally frowned upon, xp_cmdshell can get most info from the OS. Just ensure your script disables it again after calling it like so

exec sp_configure 'show advanced options', '1'

reconfigure

exec sp_configure 'xp_cmdshell', '1'

reconfigure

exec xp_cmdshell 'wmic volume get capacity, "free space", name'

exec sp_configure 'xp_cmdshell', '0'

reconfigure

exec sp_configure 'show advanced options', '0'

reconfigure