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Multisite Exchange Organization Patching

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Imagine the following scenario where you have your Exchange Organization split in three major sites, where each site has their own domain, for instance EMEA, APAC and AMERICAS.

In each site we have CCR clusters, Hub Transport and CAS servers, all in Service Pack 1. Service Pack 2 meanwhile is released and we end up with a major doubt regarding how should we act in terms of such upgrade.

The doubt generally resides between:

  • Upgrade each site, every single role, to Service Pack 2 and only then upgrade the other sites, one by one;
  • Upgrade all the CAS servers followed by the Hub Transport servers in every single site to Service Pack 2 and only then upgrade the CCR clusters;

The answer for this is quite simple, long maybe as we need to reassure some stuff around it, but definitely it is not hard as it may initially seem.

It doesn’t matter which choice we take, as long as we upgrade first the CAS servers, especially if we are using CAS-CAS proxy. We can have servers with Service Pack 1 and others with Service Pack 2, as long as the CAS is greater (or equal) to the mailbox. In terms of delays, as in timeframe for the patching operation between the first and last patches, that doesn’t really matter, as far as the versions are supported and in this case Service Pack 1  is still supported!

Another thing to take as a recommendation is that two CAS servers can have different versions as far as we do not have them in NLB or even in a CAS Array as in that case the RPC Client Access attribute in the databases will just be a virtual name, as so everything within that virtual name (NLB or CAS Array) need to be consistent in terms of versions… This exclude the time that takes the update of all servers in the NLB or CAS Array obviously.

This apply to all builds, or at least to all the Release Updates and Service Packs supported at the moment. Obviously the CAS servers on the internet facing site must always be the first servers to upgrade, otherwise you definitely break the OWA.

Finally if you upgrade a whole site first, if it is the internet-facing site, there is no issue in having the others sites with lower versions.