Question: I'm upgrading from DirSync to Azure AD Connect in a parallel deployment and when I initially set up DirSync I synced all OUs. Now I want to only sync a subset of them. What is the best way to make this change while doing an upgrade?
Answer: You will want to make this change BEFORE you upgrade. The reason being is if you select only the subset of OUs, Azure AD Connect will not be aware of the OUs you have unselected and these objects that are already synced to Azure AD will remain in Azure AD as unmanaged objects. You'll want to delete the unwanted objects BEFORE you start the migration.
Answer: I think we all know the answer to this. No absolutely not. You need to fix the issues. I would recommend starting with IDFix, https://www.microsoft.com/en-us/download/details.aspx?id=36832 The KB can be used as a TEMPORARY measure to allow synchronization to finish processing all the objects before the error is reached and then do a cloud filter until the objects are fixed. Moral of the story, you need to fix your objects.
Question: I have Azure AD Connect using Password Sync. There is no federation like ADFS. If their AD on prem account has a password change or is disabled, do I need to wait up to 3 hours for this to take place or should I force a manual sync?
Answer: Password Sync takes place every 2 minutes. The disabled user would be part of the normal sync. If you need to remove access quicker you are able to go to the portal, click on the user and hit disable.
Question: I lost all of my transformations and had to re-create them when upgrading to a newer version of the sync engine. Now I am hesitant to upgrade again. What can I do to mitigate this from re-occurring?
Answer: The AD Connect sync engine is designed to preserve any custom rules when performing an in-place upgrade.
You can create a copy of the default rule, edit that copy, and disable the default rule instead. If you are still hesitant to upgrade because of your previous experience, you can setup a separate sync engine in "Staging mode" and ensure that it is setup in your desired state before you start syncing.
You can find the documentation on how to do this here in the Azure AD Connect sync: Operational tasks and consideration article on Azure.com We hope you've found this post and this series to be helpful.