Herein you will find either the definitive documentation on an HBase topic as of its standing when the referenced HBase version shipped, or it will point to the location in Javadoc or JIRA where the pertinent information can be found. The source for this guide can be found in the _src/main/asciidoc directory of the HBase source.
Your cluster’s operation can hiccup because of any of a myriad set of reasons from bugs in HBase itself through misconfigurations — misconfiguration of HBase but also operating system misconfigurations — through to hardware problems whether it be a bug in your network card drivers or an underprovisioned RAM bus (to mention two recent examples of hardware issues that manifested as "HBase is slow").
You will also need to do a recalibration if up to this your computing has been bound to a single box.
Here is one good starting point: Fallacies of Distributed Computing.
To protect existing HBase installations from new vulnerabilities, please do not use JIRA to report security-related bugs.
Instead, send your report to the mailing list [email protected], which allows anyone to send messages, but restricts who can read them.