WITH g AS
(
	SELECT DB_NAME(mf.database_id) AS database_name, mf.physical_name,
		LEFT(mf.physical_name, 1) AS drive_letter,
		vfs.num_of_writes,
		vfs.num_of_bytes_written/1048576 AS MBwritten,
		vfs.io_stall_write_ms,
		mf.type_desc, vfs.num_of_reads, vfs.num_of_bytes_read,
		vfs.io_stall_read_ms,
		vfs.io_stall, vfs.size_on_disk_bytes
	FROM sys.master_files mf
	JOIN sys.dm_io_virtual_file_stats(NULL, NULL) vfs
	ON mf.database_id=vfs.database_id AND mf.file_id=vfs.file_id
	-- order by vfs.num_of_bytes_written desc)
)
SELECT database_name, drive_letter, MBwritten, 
	percentage=RTRIM(CONVERT(DECIMAL(5,2), MBwritten*100.0/(SELECT SUM(MBwritten) FROM g))) 
	--- where drive_letter='R')))
	+ '%',
	io_stall_read_ms, io_stall_write_ms
FROM g -- where drive_letter='R'
ORDER BY MBwritten DESC