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Should I backup my OAB Public Folder Server?

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We all know that in HMC environment has recommended that we should have dedicated Exchange Public Folder servers hosting purely just the Offline Address Books (OAB). You need the OAB Public Folder server in HMC 3.5 and HMC 4.0 if you want to allow your users to have the capacity to still access the address book while they are offline.

In HMC 4.5, it is optional. However if you want to support Outlook 2003 clients (let's call it legacy Outlook clients) running in cached mode and you want OAB to be downloadable and be available while they are disconnected, then you will need the OAB Public Folder Server. If your environment is only going to support Outlook 2007 and above, then you do not need OAB Public Folder server because you will be distributing OABs through Client Access Server using Web-based distribution model instead.

All of us know that it is essential to back up the mailbox server and the public folder server. However, when it comes to public folder servers that host purely just the OABs, most will tell you that you don't need it. So, what do you think? Do you think we need to backup those databases too?

Let's look at why it is not needed first. The reason given is simple; you don't really need to back them up because you can always re-run the process to regenerate all the offline address books. Yes, it is true but only to some extents.

I have a problem of not backing up the OAB Public Folder Server. Reason is this, depending on the environment, the regeneration process will take quite a while and depending on your environment it may cause some Active Directory performance issues too during the regeneration process.

So, how long does it really take? Now, when you run through your HEOABUpdate log (which is in C:\Program Files\Microsoft Hosting\Provisioning\Exchange OAB Update\logs), you may find that the OAB Update process consumes a really short time for each company in your environment. You may also find the same if you are to run Update-OfflineAddressBook cmdlet in the Exchange Management Shell, it will complete without error almost immediately. However, it should be noted that, that is only the submission process. What happens is that the cmdlet only submits the request to the queue of the OAB generation server. The OABgen server will then take over and process the queue and generate the OABs. If any error is encountered, you will find it in the event log instead of getting the error while executing the cmdlet.

We have seen in some environments where the number of address lists and global address lists are huge, it may take as much as 2-3 minutes per OAB. Doesn’t sound like a big deal, right? Right but think about this, if you need to rebuild the whole OAB server, and you have 1000 OABs in the server, you may potentially need about 30 hours to complete the rebuild.

So, the question really comes back to what are your RTO and your RPO? If you think you can live with the above and that your helpdesk won’t mind explaining to your customers why they are receiving error in their Outlook while doing Send/Receive during that period, then I say, yeah, you don’t need to back them up. If not, my recommendation is, let's back them up. After all, how difficult is it to back up that small Public Folder database that host only the OABs?

Cheers.

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