Migrating an Exchange 2010 Generated OAB to Exchange 2013

Question

Hello,
I'm trying to find some information on how to migrate the offline address book from Exchange 201o to Exchange 2013, but I'm having a lot of trouble finding anything at all that is of any use, so I was hoping the experts here might be able to offer some advice.
I have an environment where all mailboxes are on Exchange 2010. Recently I introduced Exchange 2013 into the environment, so we have a co-existence situation. At the moment we run a multi-tenant system that has over 1600 OABs, all assigned to various customers
using Address Book Policies. Soon, I will be starting to migrate mailboxes to 2013, so I was looking at what closing down activity is necessary to remove 2010, with one of the tasks being the transferral of the OAB. I understand the arbitration mailbox bit
and how it works on 2013, equally I understand the 2010 bit and how that works, but it's the transition from using a 2010 OAB to using a 2013 OAB that I don't understand. From what I've read to date it seems like the only option might be to totally recreate
the OABs in 2013. Surely this can't be the only way, can it? This is going to be a mammoth task for me if that's the case. Can I therefore just ask whether anyone knows anything about this in something other than a basic almost default environment where everyone
only uses a single OAB and its an easy task?
I have seen another post here in the forums about this:
http://social.technet.microsoft.com/Forums/en-US/121f282c-1ff4-401d-9257-5dfbf17d4a5c/going-from-exchange-2010-to-exchange-2013-what-about-my-2010-oab?forum=exchangesvrgeneral
I didn't fully understand the answer though. In the article above it states:
"NO you don't have to move, all OAB's have already been created and stored in your OABGEN mailbox and are safe there Updating 12 times a day. The way OABs are stored has changed and its even better. all OABs have gone into <Default Offline
Address Book 2013>."
But that still doesn't detract from the fact that whether there's any kind of sync going on or not, I still have 1600+ OABs generated by a 2010 server, and either I can't uninstall the last 2010 server because of that, or I delete the OAB, in which case
I lose the OAB anyway. Or is the articles trying to state that I don't need multiple OABs because it's all in the default, and that even if I use multiple ABPs then each one should use the default OAB? That doesn't sound right.
I have tested doing it the manual way in a lab (by that I mean creating a new OAB in 2013, then replacing a test user's OAB in the ABP assigned to them). That seems to work, but I don't want to have to do it that way for everyone if I can avoid it.
Any help would be much appreciated on this. 

Answer 1

Ok, so I think I've got an answer to my own question here. Based on my own testing to find out how easy it would be to have to do a delete/recreate of the OABs in 2013 (given that I have over 1600 ABPs and corresponding OABs in a multi-tenant environment),
I've got this:
Identify ABPs and which 2010 OABs they use using Get-AddressBookPolicy
Identify which address lists the 2010 OABs use using Get-OfflineAddressBook
Create new OABs (maybe same name but putting '2013' on the end or something)
Switch the OAB defined in the ABP using Set-AddressBookPolicy with the -OfflineAddressBook parameter
Have I got that right? So actually, not too hard really (if I'm right of course), because I don't have to build any new GALs or ALs based on specific extensionAttribute values, because it's not necessary.