Measure the I/O load on database files and file group using fn_virtualfilestats

Here is the script which can give you SQL Server file IO Statistics for each file and file group. Using this data you can find out sql server read/write performance of your disks.

DECLARE @TotalIO    BIGINT,
    @TotalBytes BIGINT,
    @TotalStall BIGINT

SELECT @TotalIO  = SUM(NumberReads + NumberWrites),
       @TotalBytes = SUM(BytesRead + BytesWritten),
       @TotalStall = SUM(IoStallMS)
FROM ::FN_VIRTUALFILESTATS(NULL, NULL)

SELECT [DbName] = DB_NAME([DbId]),
      (SELECT name FROM sys.master_files
        WHERE database_id = [DbId]
              and FILE_ID = [FileId]) filename,
    [%ReadWrites]       = (100 * (NumberReads + NumberWrites) / @TotalIO),
    [%Bytes]        = (100 * (BytesRead + BytesWritten) / @TotalBytes),
    [%Stall]        = (100 * IoStallMS / @TotalStall),
    [NumberReads],
    [NumberWrites],
    [TotalIO]       = CAST((NumberReads + NumberWrites) AS BIGINT),
    [MBsRead]       = [BytesRead] / (1024*1024),
    [MBsWritten]        = [BytesWritten] / (1024*1024),
    [TotalMBs]      = (BytesRead + BytesWritten) / (1024*1024),
    [IoStallMS],
    IoStallReadMS,
    IoStallWriteMS,
    [AvgStallPerIO]     = ([IoStallMS] / ([NumberReads] + [NumberWrites] + 1)),
    [AvgStallPerReadIO] = (IoStallReadMS / ([NumberReads] + 1)),
    [AvgStallPerWriteIO]= (IoStallWriteMS / ( [NumberWrites] + 1)),

    [AvgBytesPerRead]  = ((BytesRead) / (NumberReads + 1)),
    [AvgBytesPerWrite] = ((BytesWritten) / (NumberWrites + 1))
FROM ::FN_VIRTUALFILESTATS(NULL, NULL)
ORDER BY dbname