We are facing a common problem, common because We have researched and lot of other customers are facing it.
On our CAS servers w3wp process is taking too much CPU resouces
So just launch task manager : From View add command line
Now see which pool is taking the lot of resources, so you will reveal it is active sync pool :)
getting to the point now, it's a bug in calendar implementation of IOS 6.1 devices(iphone/Ipads).
You can check by running the script provided by Exchange team to find out which devices are hitting hard on your servers.
below are the links that can be referred:
Result would be like :-
Permanent resolution is IOS7 but for now what we have done is, created the new throttling policy --> restricted the below parameters to 30 and applied it to users that have hits more than 1500.
EASPercentTimeInAD : 30
EASPercentTimeInCAS : 30
EASPercentTimeInMailboxRPC : 30
Create Throttling policy
New-ThrottlingPolicy -Name iOS61users -EASPercentTimeInCAS 30 -EASPercentTimeInAD 30 -EASPercentTimeInMailboxRPC 30
Apply Throttling policy
Get-Mailbox "LAB\Vikassukhija" | Set-Mailbox –ThrottlingPolicy "iOS61users"
These threshold settings can vary as per environment.
If you want to apply the policy to users in bulk than use the below script that I had created.