I’ve been involved in a large 2500 seat Exchange 2010 to Exchange 2013 migration and consolidation project recently. During the mailbox moves, I found that often the move requests were being stalled with a status of RelinquishedWLMStalled. I tried to change many things to improve the migration including modifying the MSExchangeMailboxReplication.exe.config file to change the ExportBufferSize, MaxActiveJobsPerSourceMailbox and MaxActiveJobsPerTargetMailbox. All this didn’t seem to make a major difference until I stumbled upon the fact that the Workload Management (WLM) facility within Exchange was what was causing the “problem”. I say problem because the WLM is designed to ensure that the server does not get overloaded by any one aspect and gives preference for operations to those operations that are user facing – ie accessing their email. In this scenario moving a mailbox is deemed a much lower priority than anything else. I made the following reg change, and then rebooted my server (probably could have gotten away with restarting the MRS services, but I needed to reboot anyway.
After using this registry mod, I found I was able to flatline the clients WAN environment over a weekend and really move mail very fast. BE CAREFUL WITH THIS MOD. The end result for us was that we were able to effective move and consolidate 3TB of mail from a number of Exchange 2010 servers into our Exchange 2013 environment within 3 weeks total. To give you an idea of link speed, the fastest link was a 40Mb/s link to head office, and the remote 2010 servers were from 8Mb/s to 20Mb/s speeds.
As I said – use with caution, but it might really help you move your mail faster if you need it.