hadoop Protocol message was too large. May be malicious. Use CodedInputStream.setSizeLimit() to increase the size limit
Solution 1:
The answer to this question was already provided in the comments:
My hadoop 2.7.0 cluster was not starting. I had to recompile protobuf-2.5.0, changing com.google.protobuf.CodedInputStream#DEFAULT_SIZE_LIMIT to 64 << 24. Then I modified hdfs-site.xml to include ipc.maximum.data.length 134217728 and now it seems back up.