How to diagnose IO Problems

Recently our production database began experiencing very poor I/O
performance. How do I begin to narrow down the queries or tables that are
affecting this?
It would be useful to know which platform is in use (SQL 2000 or SQL 2005),
because there are some changes in the way you can investigate.
1) Verify the server situation: is there any fragmentation problem
(especially on the pagefile)?
2) verify the cause of the wait, using DBCC SQLPERF(WAITSTATS) in SQL 2000
or querying the sys.dm_os_wait_stats DMV in SQL 2005;
you should be able to identify the correct area of investigation:
there is a simple example of using the SQL 2005 DMV:
SELECT
wait_type,
waiting_tasks_count,
wait_time_ms,
max_wait_time_ms,
signal_wait_time_ms
FROM sys.dm_os_wait_stats
ORDER BY wait_type
3) Get some useful information about the involved resources using
master.dbo.sysperfinfo in SQL 2000 or sys.dm_os_performance_counters in SQL
2005;
4) Use ::fn_virtualfilestats in SQL 2000 or sys.dm_io_virtual_file_stats to
identify the more stressed database files:
here is an example of using the DMO:
WITH DBIO AS
SELECT
DB_NAME(IVFS.database_id) AS db,
CASE WHEN MF.type = 1 THEN 'log' ELSE 'data' END AS file_type,
SUM(IVFS.num_of_bytes_read + IVFS.num_of_bytes_written) AS io,
SUM(IVFS.io_stall) AS io_stall
FROM sys.dm_io_virtual_file_stats(NULL, NULL) AS IVFS
JOIN sys.master_files AS MF
ON IVFS.database_id = MF.database_id
AND IVFS.file_id = MF.file_id
GROUP BY DB_NAME(IVFS.database_id), MF.type
5)Pay attention to the transaction log of the critical databases (location,
number of virtual logs, etc.) and dedicate special attention to the tempDB
(it is usually the more stressed file of a SQL Instance); look at cursor
usage, temporary tables and table variables.
6)Finally, when you have sufficient elements of investigation, you can
profile your instance or your databases with a SQL Profiler trace using the
appropriate event classes.
In this moment i think is premature suggest you which kind of profiling
could be the best: you should decide it when you will have gathered all of
the infos from the previously described steps.
Gilberto
"Dan" wrote:

> Recently our production database began experiencing very poor I/O
> performance. How do I begin to narrow down the queries or tables that are
> affecting this?