How to examine IO subsystem latencies from within SQL Server

gistfile1.txt

--http://www.sqlskills.com/blogs/paul/how-to-examine-io-subsystem-latencies-from-within-sql-server/
SELECT
    [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,
    [Latency] =
        CASE WHEN ([num_of_reads] = 0 AND [num_of_writes] = 0)
            THEN 0 ELSE ([io_stall] / ([num_of_reads] + [num_of_writes])) END,
    [AvgBPerRead] =
        CASE WHEN [num_of_reads] = 0
            THEN 0 ELSE ([num_of_bytes_read] / [num_of_reads]) END,
    [AvgBPerWrite] =
        CASE WHEN [num_of_writes] = 0
            THEN 0 ELSE ([num_of_bytes_written] / [num_of_writes]) END,
    [AvgBPerTransfer] =
        CASE WHEN ([num_of_reads] = 0 AND [num_of_writes] = 0)
            THEN 0 ELSE
                (([num_of_bytes_read] + [num_of_bytes_written]) /
                ([num_of_reads] + [num_of_writes])) END,
    LEFT ([mf].[physical_name], 2) AS [Drive],
    DB_NAME ([vfs].[database_id]) AS [DB],
    [mf].[physical_name]
FROM
    sys.dm_io_virtual_file_stats (NULL,NULL) AS [vfs]
JOIN sys.master_files AS [mf]
    ON [vfs].[database_id] = [mf].[database_id]
    AND [vfs].[file_id] = [mf].[file_id]
-- WHERE [vfs].[file_id] = 2 -- log files
-- ORDER BY [Latency] DESC
-- ORDER BY [ReadLatency] DESC
ORDER BY [WriteLatency] DESC;
GO

SELECT
[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,
[Latency] =
CASE WHEN ([num_of_reads] = 0 AND [num_of_writes] = 0)
THEN 0 ELSE ([io_stall] / ([num_of_reads] + [num_of_writes])) END,
[Latency Desc] =
CASE
WHEN ([num_of_reads] = 0 AND [num_of_writes] = 0) THEN 'N/A'
ELSE
CASE WHEN ([io_stall] / ([num_of_reads] + [num_of_writes])) < 2 THEN 'Excellent'
WHEN ([io_stall] / ([num_of_reads] + [num_of_writes])) < 6 THEN 'Very good'
WHEN ([io_stall] / ([num_of_reads] + [num_of_writes])) < 11 THEN 'Good'
WHEN ([io_stall] / ([num_of_reads] + [num_of_writes])) < 21 THEN 'Poor'
WHEN ([io_stall] / ([num_of_reads] + [num_of_writes])) < 101 THEN 'Bad'
WHEN ([io_stall] / ([num_of_reads] + [num_of_writes])) < 501 THEN 'Yikes!'
ELSE 'YIKES!!'
END
END,
[AvgBPerRead] =
CASE WHEN [num_of_reads] = 0
THEN 0 ELSE ([num_of_bytes_read] / [num_of_reads]) END,
[AvgBPerWrite] =
CASE WHEN [num_of_writes] = 0
THEN 0 ELSE ([num_of_bytes_written] / [num_of_writes]) END,
[AvgBPerTransfer] =
CASE WHEN ([num_of_reads] = 0 AND [num_of_writes] = 0)
THEN 0 ELSE
(([num_of_bytes_read] + [num_of_bytes_written]) /
([num_of_reads] + [num_of_writes])) END,
[IOPS] = [num_of_reads] + [num_of_writes],
LEFT([mf].[physical_name], 2) AS [Drive],
DB_NAME([vfs].[database_id]) AS [DB],
[mf].[physical_name]
FROM
sys.dm_io_virtual_file_stats(NULL, NULL) AS [vfs]
JOIN sys.master_files AS [mf]
ON [vfs].[database_id] = [mf].[database_id]
AND [vfs].[file_id] = [mf].[file_id]
-- WHERE [vfs].[file_id] = 2 -- log files
ORDER BY [Latency] DESC
-- ORDER BY [ReadLatency] DESC
-- ORDER BY [WriteLatency] DESC;
GO

------updated query Get IOPS details........