I was helping a new user trying to use Accumulo. They managed to set up HDFS, running on hdfs://localhost:8020. But they didn't set it up with specific settings, and just used the default port. Accumulo worked initially, but would not allow a bulk import.
During the bulk import process, the servers need to move the files into the accumulo volumes, but keeping the volume the same. This makes the move efficient, since nothing is copied between namespaces. In this case it refused the import because it could not find the correct volume.
Accumulo needs to be more nuanced when comparing hdfs://localhost:8020, and hdfs://localhost.