I have been asked to give percentages of read vs write traffic on a SQL Cluster and I cannot readily think of a way to accomplish this without running profiler or another like tool.
Answer by Kev Riley ·
Glenn Berry has some good scripts in his Diagnostic Information Queries: https://www.sqlskills.com/blogs/glenn/
You can see reads/writes per Drive:
-- Drive level latency information (Query 29) (Drive Level Latency) -- Based on code from Jimmy May SELECT tab.[Drive], tab.volume_mount_point AS [Volume Mount Point], CASE WHEN num_of_reads = 0 THEN 0 ELSE (io_stall_read_ms/num_of_reads) END AS [Read Latency], CASE WHEN num_of_writes = 0 THEN 0 ELSE (io_stall_write_ms/num_of_writes) END AS [Write Latency], CASE WHEN (num_of_reads = 0 AND num_of_writes = 0) THEN 0 ELSE (io_stall/(num_of_reads + num_of_writes)) END AS [Overall Latency], CASE WHEN num_of_reads = 0 THEN 0 ELSE (num_of_bytes_read/num_of_reads) END AS [Avg Bytes/Read], CASE WHEN num_of_writes = 0 THEN 0 ELSE (num_of_bytes_written/num_of_writes) END AS [Avg Bytes/Write], 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 AS [Avg Bytes/Transfer] FROM (SELECT LEFT(UPPER(mf.physical_name), 2) AS Drive, SUM(num_of_reads) AS num_of_reads, SUM(io_stall_read_ms) AS io_stall_read_ms, SUM(num_of_writes) AS num_of_writes, SUM(io_stall_write_ms) AS io_stall_write_ms, SUM(num_of_bytes_read) AS num_of_bytes_read, SUM(num_of_bytes_written) AS num_of_bytes_written, SUM(io_stall) AS io_stall, vs.volume_mount_point FROM sys.dm_io_virtual_file_stats(NULL, NULL) AS vfs INNER JOIN sys.master_files AS mf WITH (NOLOCK) ON vfs.database_id = mf.database_id AND vfs.file_id = mf.file_id CROSS APPLY sys.dm_os_volume_stats(mf.database_id, mf.[file_id]) AS vs GROUP BY LEFT(UPPER(mf.physical_name), 2), vs.volume_mount_point) AS tab ORDER BY [Overall Latency] OPTION (RECOMPILE);
or by database file
-- Calculates average stalls per read, per write, and per total input/output for each database file (Query 30) (IO Stalls by File) SELECT DB_NAME(fs.database_id) AS [Database Name], CAST(fs.io_stall_read_ms/(1.0 + fs.num_of_reads) AS NUMERIC(10,1)) AS [avg_read_stall_ms], CAST(fs.io_stall_write_ms/(1.0 + fs.num_of_writes) AS NUMERIC(10,1)) AS [avg_write_stall_ms], CAST((fs.io_stall_read_ms + fs.io_stall_write_ms)/(1.0 + fs.num_of_reads + fs.num_of_writes) AS NUMERIC(10,1)) AS [avg_io_stall_ms], CONVERT(DECIMAL(18,2), mf.size/128.0) AS [File Size (MB)], mf.physical_name, mf.type_desc, fs.io_stall_read_ms, fs.num_of_reads, fs.io_stall_write_ms, fs.num_of_writes, fs.io_stall_read_ms + fs.io_stall_write_ms AS [io_stalls], fs.num_of_reads + fs.num_of_writes AS [total_io], io_stall_queued_read_ms AS [Resource Governor Total Read IO Latency (ms)], io_stall_queued_write_ms AS [Resource Governor Total Write IO Latency (ms)] FROM sys.dm_io_virtual_file_stats(null,null) AS fs INNER JOIN sys.master_files AS mf WITH (NOLOCK) ON fs.database_id = mf.database_id AND fs.[file_id] = mf.[file_id] ORDER BY avg_io_stall_ms DESC OPTION (RECOMPILE);
Obviously the data available in these DMVs is subject to the usual caveats about how long the server has been up etc.