Bennett Adelson Technical Blog

Bennett Adelson Technical Blog

Office 365 E-Mail Migration Performance


Last month Microsoft released a document outlining Exchange Online Migration Performance.  You can find the article here. While it’s not a bad read at 26 pages, I will highlight some of the important pieces.

It’s always important to keep in mind the data and how it will get to Office 365 when considering moving to Exchange Online.  Depending on the size of your total email data, the source mail platform, and the tool you will be using to migrate the data the time per user can vary drastically.

Let’s take a look at the following chart provided by Microsoft that highlights some of the throttling.

Migration tool Migration   method User   throttling Migration-service   throttling Office 365   resource health-based throttling Observed   average throughput per hour and per client (if applicable)
Native   O365/Simple Migration IMAP4   migration

No

Yes

Yes

5-10 gigabyte (GB) (50 concurrency)

Native   O365/Simple Migration Cutover   Exchange migration

No

Yes

Yes

5-10 GB (50 concurrency)

Native   O365/Simple Migration Staged   Exchange migration

No

Yes

Yes

5-10 GB (50 concurrency)

Native O365 Hybrid   migration

No

Yes

Yes

10-15 GB (per On-premise Exchange 2010   CAS)

Third Party MAPI

Yes

No

Yes

0.5-1 GB

Third Party EWS

No

Yes

Yes

5-10 GB

Client   Uploading Outlook

Yes

No

Yes

0.5 GB

As you can see there are a few different caps depending on what type of migration you are performing and what type of tool you are using.  For example, the native Office 365 tools in the Exchange Control Panel can perform either a Simple(think IMAP), Cutover(from Exchange on Prem) and Staged(Also from On prem).  Hybrid migration, in which a 2010 Client Access Server where Hybrid mode has been configured, is the fastest means to migrate which makes sense given Microsofts subtle push to have people with Exchange on prem migrate in this fashion.  If you’re using a 3rd party tool be sure it can use Exchange web services to connect to Office 365.

By far the slowest method of migration is 3rd party MAPI and Client uploading.  Keep these in mind because if your migration plan was export/import .PST files using either in house methods or some of the *free* migration tools out there you need to understand just how slow they will be.  Typically this type of method should only really be used in which the number of users is very small.

Looking over these #s that they’ve listed and I would say this is somewhat what I’ve observed performing migrations in the field.  For me though, the biggest factor is what platform you are migrating off of and the performance of that server and your network.  Some IMAP migrations from older systems or on servers that have been around for years can take much longer than you would see from other IMAP migrations such as Gmail.  I’ve seen 10 user mailboxes averaging 3gb each take 12 hours to complete in total with max concurrency set to 5(which according to the chart should take 3-4 hours).  It’s always important to pilot and test your migration to get expectations before planning production schedules and dates.

As I mentioned earlier Hybrid Migrations do seem to be the direction Microsoft is pushing companies to if they have Exchange on-premise.  My only concern with this is that it can be extremely complicated for Administrators who do not have a lot of experience with Exchange 2007+ and how web services and autodiscover work.  Putting in Exchange 2010 CAS with hybrid in an Exchange 2003 environment can be complex for a seasoned Exchange administrator, much less one that’s only experience is in Exchange 2003.  With Exchange 2010 SP2 it has made that process somewhat easier(wizard), but it still requires knowing how all the services work to get it right.  My advice is carefully determine what Hybrid mode offers your company and if those additional benefits are worth the extra efforts involved in implementing it.

Peter Gleek

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