Migrations between messaging systems, depending on the environment, can be fraught with plenty of hurdles that need to be overcome. Hurdles like design decisions, sizing the hardware correctly, managing user expectations, transitioning certain pieces without issue, etc.
If you were upgrading to Exchange 2013 from Exchange 2007, you may have noticed that the migration process was extremely slow. Apparently there was a bug in the newer CUs for Exchange 2013 that was causing a bottleneck to occur.
You can read about the details of the fix here:
https://support.microsoft.com/en-us/kb/3107337
A similar performance issue affected email deliveries as well:
https://support.microsoft.com/en-us/kb/3088487
If you are installing Exchange 2013 soon and you are migrating from Exchange 2007, make sure you SKIP CU10. Although I have not verified the performance of CU11 I do know that I did not experience the aforementioned issue in CU9, but a recent CU10 migration revealed the slowness issue. I was able to speed migrations in CU10 with some tweaks to the “MSExchangeMailboxReplication.exe.config” file to get through the migration and was only made aware of the setting override mentioned in the article after my migration was complete. Do not use the fix mentioned in KB3107337 unless you have to stay on CU10.
If you can avoid CU10, please do so.
If you are going to CU11, make sure to read this EHLO Blog Article on some changes in PowerShell that will affect your migration.
A blog about PowerShell! … and Office 365
