I got an email today asking me as to how long the upgrade from Exchange 2010 to SP2 should take. The Exchange admin who sent me the email mentioned that the process was too “slow” for him and was wondering what the issue was.
I should state that there is nothing wrong in the process and that the steps executed as part of the upgrade takes a while to complete. Why does it take this long, you may ask. The reason why it takes longer is because it has to do two schema upgrades. Yes, you heard me right, two!
The first one is upgrading the Active Directory schema, adding more classes and attributes to AD. The second one is the Exchange database schema upgrade. With SP2, the schema of the database is “changed” or “upgraded”. This was the case with 2010 SP1 as well. In short, whenever you jump to a service pack from a lower one (including RTM), the database schema is changed.
For the same reason, a database running on Exchange 2010 SP2 server cannot be mounted on any lower level 2010 mailbox servers (RTM or SP1).
Hope this clears the confusion around “slowness” in the upgrade process. Just leave the setup running & as long as you don’t get any errors, you are good 
John Mitchell July 3, 2012 at 4:02 pm
Don’t forget that if CRL checking isn’t disabled in the Advanced settings of IE, that this can greatly lengthen the update time as well.
Rajith Enchiparambil July 3, 2012 at 7:09 pm
That normally happens with update rollup installations John. But sure, something to bear in mind.
Scott July 4, 2012 at 12:15 am
Thanks for the post, one quick question though when you say that the database schema is updated what happens in a DAG? If I upgrade a passive DAG member to SP2 does that update the database and if so why does the database continue to run on the active node?
Cheers
Scott.
Rajith Enchiparambil July 4, 2012 at 9:08 am
Hi Scott,
You need to be really careful while updating the DAG. Update your passive server first, flip the databases and then the initially active one. But, that catch is you need to be fast. If you update the passive server, flip the database and your “upgraded” server fails before you patch the initially active server, you are in trouble.
Databases mounted on SP2 servers cannot be mounted on SP1 servers!
Thanks.
Ryan March 8, 2013 at 4:35 pm
When upgrading a DAG, when does the conversion take place? If I upgrade a passive node, are the databases upgraded then? Or does it happen when I first move a database to a member that has been upgraded?
Rajith Enchiparambil March 13, 2013 at 11:58 pm
HI Ryan,
I think once you make a copy active on the “upgraded” server, it can’t be mounted on a server which doesn’t have the correct SP level.