I was upgrading a client’s environment from FIM2010 R2 to MIM2016, during the upgrade of the Synchronization service, the installer appeared stuck, I waited for over an hour, there was no activity and no progress update. I checked the msi installation log, and found the last activity was CustomAction = SetPermissionEval, ActionType=3073. Other than this, there was no errors or any indication of failures.
According to this TechNet article, SetPermissionEval sets access permission (ACLs) for file folders, registry, DCOM launch/access permission and WMI.
ExtensionsCache
So I opened the Process Monitor, I discovered the reason was the hidden folder Microsoft Forefront Identity Manager\2010\Synchronization Service\ExtensionsCache, this directory contained over 260,000 folders with approximately 2 million objects, the SetPermissionEval custom action was applying ACL on each of them!
I couldn’t find the exact purpose for the ExtensionsCache, there is no Microsoft documentation on it nor any mention in the official upgrade guidance or best practice, however by looking at the contents of the folder, I suspect FIM/MIM creates these folders when running synchronisation or export using custom code based extension rules.
Based on an earlier forum post, I decided to delete the contents in this folder
Once all the items are deleted, I restarted the synchronization service upgrade, the upgrade continued and finished without delay.
I still don’t understand why the installer file should try to set the file permission in the cache directory, when the whole directory content could be removed without problem, why brother?
Anyway if you are upgrading or patching your FIM or MIM instance, it might be worthwhile to check your ExtensionsCache hidden directory, if you have too many folders there, stop the synchronization service and delete those cache folders to avoid this problem.