Q:

Hbase NotServingRegionException: Region is not online

One of my Hbase regionservers went offline because of HDFS going into Safe Mode -- or couldn't come back online because of Safe Mode (chicken-egg issue) -- so I fixed this and got the region server working again, but then I could no longer query Hbase.  I received an error, NotServingRegionException: Region is not online: <my table>...
Another SO Post and similar blog post suggested deleting some entries from Zookeeper, but this sounded like a potentially dangerous route to go, especially since our error messages didn't match.
What is a safe solution to this issue?

A:

The solution that worked for me was to simply restart Hbase Master.
(On Ubuntu w CDH4): sudo service hbase-master restart

