Continuation to my previous post on FSMO roles.
If the Schema Master role is down it isn’t crucial that it be brought up immediately. This role is only used when making schema changes.
If the Domain Master role is down it isn’t crucial that it be brought up immediately. This role is only used when adding/ removing domains and new partitions.
If the Infrastructure Master role is down two things could be affected – groups containing users from other accounts, and you can’t run
adprep /domainprep. The former only runs every two days, so it isn’t that crucial. Moreover, if your domain has Recycle Bin enabled, or all your DCs are GCs, the Infrastructure Master role doesn’t matter any more. The latter is only run when you add a new DC of a later Windows version than the ones you already have (see this link for what
Adprep does for each version of Windows) – this doesn’t happen often, so isn’t crucial.
If the RID Master role is down RID pools can’t be issued to DCs. But RIDs are handed out in blocks of 500 per DC, and when a DC reaches 250 of these it makes a request for new RIDs. So again, unless the domain is having a large number of security objects being created suddenly – thus exhausting the RID pool with all the DCs – this role isn’t crucial either.
When I keep saying a role isn’t crucial, what I mean is that you have a few days before seizing the role to another DC or putting yourself under pressure to bring the DC back up. All these roles are important and matter, but they don’t always need to be up and running for the domain to function properly. Also, if a DC holding a role is down and you seize the role to another DC, it’s recommended not to bring the old DC up – to avoid clashes. Better to recreate it as a new DC.
Lastly, the PDC Emulator role. This is an important role because it is used in so many areas – for password chaining, for talking to older DC, for keeping time in the domain, for GPO manipulation, DFS (if you have enabled optimize for consistency), etc. Things won’t break, and you can transfer many of the functions to other DCs, but it’s better they all be on the PDC Emulator. Thus for all the roles the PDC Emulator is the one you should try to bring back up first. Again, it’s not crucial, and things will function well while the PDC Emulator, but it is the most important role of all.