question

First of all define "My Sql server 2012 performance is very slow" - is it a particular query or bunch of queries that are "slow" - if so - look at the execution plans to see what is taking the time. If the whole server is "slow" - i..e at the Windows level, then is it physical or virtual? If virtual what else is on the host? What power settings do you have in the OS and in BIOS - balanced or high performance? Looking at the top wait type in isolation can be confusing - there will always be a top one - has this changed? Increased? Typically PAGEIOLATCH_SH indicates that SQL is waiting on IO, but that doesn't mean the IO performance is bad, it might be that every table is accessed via a table scan instead of index seeks? Read Paul Randal's article on troubleshooting this here : https://sqlperformance.com/2014/06/io-subsystem/knee-jerk-waits-pageiolatch-sh There's lots of directions to take this, so try and focus on what you *know*