Physical design covers several related aspects of adjustments to the databases, but deep down it's all about disk IO across the various files. Adding server memory nowadays is a fast and inexpensive affair, so the limiting operational performance in the host of most database systems is the IO throughput. Fast IO can be achieved numerous ways, but once you've established a baseline for the physical hardware and make sure you don't have any bottlenecks in disk controllers or bandwidth to your NAS, then what remains is spreading out the active database files across various drives and controllers to maximize the IO parallelism.
I use a couple different management queries to identify places where files should be split. These two queries below tell you where your usage is heaviest on your SQL instance:
WITH IOFORDATABASE ASThe files that pop out from this with the highest stall percentages should likely be split and spread. Of course you need to pay special attention to tempDB as it gets shared across all of the applications running on each particular instance (I'll have more to say about allocating tempDB in a later post).
DB_NAME(VFS.database_id) AS DatabaseName
,CASE WHEN smf.type = 1 THEN 'LOG_FILE' ELSE 'DATA_FILE' END AS DatabaseFile_Type
,SUM(VFS.num_of_bytes_written) AS IO_Write, SUM(VFS.num_of_bytes_read) AS IO_Read
,SUM(VFS.num_of_bytes_read + VFS.num_of_bytes_written) AS Total_IO
,SUM(VFS.io_stall) AS IO_STALL
FROM sys.dm_io_virtual_file_stats(NULL, NULL) AS VFS
JOIN sys.master_files AS smf ON VFS.database_id = smf.database_id
AND VFS.file_id = smf.file_id
GROUP BY DB_NAME(VFS.database_id), smf.type
ROW_NUMBER() OVER(ORDER BY io_stall DESC) AS RowNumber
,CAST(1.0 * IO_Read/ (1024 * 1024) AS DECIMAL(12, 2)) AS IO_Read_MB
,CAST(1.0 * IO_Write/ (1024 * 1024) AS DECIMAL(12, 2)) AS IO_Write_MB
,CAST(1. * Total_IO / (1024 * 1024) AS DECIMAL(12, 2)) AS IO_TOTAL_MB
,CAST(IO_STALL / 1000. AS DECIMAL(12, 2)) AS IO_STALL_Seconds
,CAST(100. * IO_STALL / SUM(IO_STALL) OVER() AS DECIMAL(10, 2)) AS IO_STALL_Pct
ORDER BY IO_STALL_Seconds DESC;
select db_name(mf.database_id) as database_name, mf.physical_name,
left(mf.physical_name, 1) as drive_letter,
vfs.num_of_writes, vfs.num_of_bytes_written, vfs.io_stall_write_ms,
mf.type_desc, vfs.num_of_reads, vfs.num_of_bytes_read, vfs.io_stall_read_ms,
from sys.master_files mf
join sys.dm_io_virtual_file_stats(NULL, NULL) vfs
on mf.database_id=vfs.database_id and mf.file_id=vfs.file_id
order by vfs.num_of_bytes_written desc
Once you've split up and created multiple files for your heavily used logs and databases, it's time to dig into some deeper level detail. This query below shows you table IO activity on a particular database; you should select your database connection (or add a USE statement) to see the details of one database at a time.
SELECT TableName = object_name(s.object_id),This will show you which specific tables are being heavily read and written to. Not infrequently I like to take the heavyweights and move them to their own filegroup.
Reads = SUM(user_seeks + user_scans + user_lookups), Writes = SUM(user_updates)
FROM sys.dm_db_index_usage_stats AS s
INNER JOIN sys.indexes AS i ON s.object_id = i.object_id
AND i.index_id = s.index_id
WHERE objectproperty(s.object_id,'IsUserTable') = 1
AND s.database_id = DB_ID()
GROUP BY object_name(s.object_id)
ORDER BY writes DESC
You can do more IO tuning down at the query level, but that's a topic for another post.