When trying to upload files using this tool, the max upload size is 3MB (mentioned here: http://gallery.technet.microsoft.com/office/The-Migration-Dragon-for-c0880e59#content)
To increase, you need to use this button on the tool, but it was crashing for me with the following error:
Description: The process was terminated due to an unhandled exception.
Exception Info: Microsoft.SharePoint.Administration.SPUpdatedConcurrencyException
In addition to this, I was getting lots of other errors from SharePoint:
The Execute method of job definition Microsoft.SharePoint.Diagnostics.SPDiagnosticsMetricsProvider (ID 7f18b8c7-49aa-45f2-8826-67ecff862c1a) threw an exception. More information is included below.
An update conflict has occurred, and you must re-try this action….
These two errors are linked, and the solution is described here: http://support.microsoft.com/kb/939308 (although the details were slightly different on my installation, Win Server 2008 R2 and SP 2013)
To fix, you need to stop the SharePoint Timer Service, clear the configuration cache (at C:\ProgramData\Microsoft\SharePoint\Config\[guid], one folder has XML files, the other persistedfiles) by deleting all the XML files (not the folder, also the KB article mentions not to remove the cache.ini file and to edit it, but I didn’t have one), and restart the SharePoint Timer Service. The article also mentions to run a config refresh from SP admin, but I couldn’t find this, so didn’t do it, and the fix worked anyway. Might need to restart IIS as well.
(Also note, I think the max you can set the button is the value that you set for the application max file upload. SharePoint 2013 has a hard limit of 2047 MB, so you can put this value in both the SharePoint web application settings and Migrator Dragon and you’ll be able to upload large files up to 2GB. To change in SP, Central Administration > Manage Web Applications > select your application and go to General Settings > Maximum upload size)