The migration using the migration wizard fails with a session timeout, if you miss to click something within ~15 minutes. In our Nexus2 instance there are round about 250 repositories (2/3rd hosted, 1/3rd groups), 300.000 artifacts and 350G of data. OK, much data will take some time to migrate. I’ve waited around 4 hours to analyze one of the hosted repositories and here comes the bad thing: You need to stay in front of the browser to click something at least every 15 minutes before your session expires. If you miss this, the migration fails.
I commented this problem on migrating-to-nexus-repository-3-easy-peasy too.
Some details from the background:
Both Nexus instances are Docker containers, each with separate storage. So the migration must copy the data from the storage of one container to the storage of the other one.