I guess it's pretty obvious by now that I am a bit of a nerd when it comes to Exchange and Outlook performance. One area that has always felt like a black box though is migrating data into Office 365 Exchange Online service.

The problem for me was that sometimes I would be able to migrate very quickly and at other times the migration would seem much slower, even though the network availability seemed the same during both times. This made migration planning extremely difficult since it was difficult to actually understand what the constraints actually were… this obviously leads to projects over and under provisioning migration schedule time which is not a good place to be.

There was also much confusion about if Office 365 was throttling some migration types and not others.

Well, I am extremely pleased to say that a guide has been released that discusses many of these questions and also finally shows what throttling policies are being applied to which migration mechanisms.

This document is a must read for anyone planning an Office 365 migration to Exchange Online

http://community.office365.com/en-us/f/183/t/45466.aspx