http://www.sqlskills.com/blogs/paul/survey-tempdb-and-transaction-log-io-latencies/?utm_source=feedly

SELECT
	[database_id],
	[file_id],
    [ReadLatency] =
		CASE WHEN [num_of_reads] = 0
			THEN 0 ELSE ([io_stall_read_ms] / [num_of_reads]) END,
	[WriteLatency] =
		CASE WHEN [num_of_writes] = 0
			THEN 0 ELSE ([io_stall_write_ms] / [num_of_writes]) END
FROM
	sys.dm_io_virtual_file_stats (NULL, NULL)
WHERE
	[file_id] = 2 OR [database_id] = 2;
GO