Hello Gurus, I have been monitoring the disk IO issues at my enviroment.
I know the disk IO is a performance killer here.
I see there are typically no pressures on the memory and CPU never goes above 50%.
Disks in our environment are not being configured correctly. The time they were configured there was NO DBA.
The Windows Admin put every disk on the same drive on a RAID 10 volumne leaving the MDF, LDF and tempDB at the same place.
Apart from the above, I see the number of disks are not adequate too. I have asked the management to move the database files to groups like one for mdf one for LDF and one for tempDB.
I am already pulling the following information from the sys.dm_os_performance_counters:
Buffer cache hit ratio every two minutes.
PLE every two minutes.
BufferPool Through put 'Database Pages'
The following disk counters every 10 seconds (we have C drive only):
PhysicalDisk(0 C:)\% Disk Read Time
PhysicalDisk(0 C:)\% Disk Time
PhysicalDisk(0 C:)\% Disk Write Time
PhysicalDisk(0 C:)\Avg. Disk Queue Length
PhysicalDisk(0 C:)\Avg. Disk sec/Read
PhysicalDisk(0 C:)\Avg. Disk sec/Write
PhysicalDisk(0 C:)\% Idle Time
I understand there are disk issues when I check the above counters and the sys.dm_os_performance_counters data.
As an example sometimes the PLE goes below 15 minutes and we start seeing the slowness or the BufferPool Through put 'Database Pages' goes above 30 MB and we see the slowness.
Similarly I see the Avg. Disk sec/Read values start going north in excess of over a second per read/write.
Question: The management wants to know that apart from regrouping the disks if we need to add more disks, what is the correct number and what is the mathematics behing that number.
I am not sure how to say that hey we can add 20 more disks and that can to a great extent fix the IO thing.
I understand that there are other optimizations like indexes, rewriting the queries, creating multiple data files for better throughput, etc that can be done.
However, lets say we keep everything else the way they are and Just conceptually want to understand what is the ideal number of disks we need, how to go about calculating it.
Thanks in Advance for reading the long message.