Estaba ejecutando algunas pruebas con mapeadores de tablas y reductores en problemas a gran escala. Después de cierto punto, mis reductores comenzaron a fallar cuando el trabajo estaba hecho al 80%. Por lo que puedo decir al mirar los syslogs, el problema es que uno de mis cuidadores del zoológico está intentando conectarse al host local en lugar de los otros cuidadores del zoológico en el quórum.

Curiosamente, parece funcionar bien conectarse a los otros nodos cuando se está realizando el mapeo, lo que reduce el problema. Aquí hay partes seleccionadas del registro del sistema que pueden ser relevantes para descubrir qué está pasando

2014-06-27 09:44:01,599 INFO [main] org.apache.zookeeper.ZooKeeper: Initiating client connection, connectString=hdev02:5181,hdev01:5181,hdev03:5181 sessionTimeout=10000 watcher=hconnection-0x4aee260b, quorum=hdev02:5181,hdev01:5181,hdev03:5181, baseZNode=/hbase
2014-06-27 09:44:01,612 INFO [main] org.apache.hadoop.hbase.zookeeper.RecoverableZooKeeper: Process identifier=hconnection-0x4aee260b connecting to ZooKeeper ensemble=hdev02:5181,hdev01:5181,hdev03:5181
2014-06-27 09:44:01,614 INFO [main-SendThread(hdev02:5181)] org.apache.zookeeper.ClientCnxn: Opening socket connection to server hdev02/172.17.43.36:5181. Will not attempt to authenticate using SASL (Unable to locate a login configuration)
2014-06-27 09:44:01,615 INFO [main-SendThread(hdev02:5181)] org.apache.zookeeper.ClientCnxn: Socket connection established to hdev02/172.17.43.36:5181, initiating session
2014-06-27 09:44:01,617 INFO [main-SendThread(hdev02:5181)] org.apache.zookeeper.ClientCnxn: Unable to read additional data from server sessionid 0x0, likely server has closed socket, closing socket connection and attempting reconnect
2014-06-27 09:44:01,723 WARN [main] org.apache.hadoop.hbase.zookeeper.RecoverableZooKeeper: Possibly transient ZooKeeper, quorum=hdev02:5181,hdev01:5181,hdev03:5181, exception=org.apache.zookeeper.KeeperException$ConnectionLossException: KeeperErrorCode = ConnectionLoss for /hbase/hbaseid
2014-06-27 09:44:01,723 INFO [main] org.apache.hadoop.hbase.util.RetryCounter: Sleeping 
***
org.apache.hadoop.mapreduce.task.reduce.MergeManagerImpl: finalMerge called with 1 in-memory map-outputs and 1 on-disk map-outputs
2014-06-27 09:55:12,012 INFO [main] org.apache.hadoop.mapred.Merger: Merging 1 sorted segments
2014-06-27 09:55:12,013 INFO [main] org.apache.hadoop.mapred.Merger: Down to the last merge-pass, with 1 segments left of total size: 33206049 bytes
2014-06-27 09:55:12,208 INFO [main] org.apache.hadoop.mapreduce.task.reduce.MergeManagerImpl: Merged 1 segments, 33206079 bytes to disk to satisfy reduce memory limit
2014-06-27 09:55:12,209 INFO [main] org.apache.hadoop.mapreduce.task.reduce.MergeManagerImpl: Merging 2 files, 265119413 bytes from disk
2014-06-27 09:55:12,209 INFO [main] org.apache.hadoop.mapreduce.task.reduce.MergeManagerImpl: Merging 0 segments, 0 bytes from memory into reduce
2014-06-27 09:55:12,210 INFO [main] org.apache.hadoop.mapred.Merger: Merging 2 sorted segments
2014-06-27 09:55:12,212 INFO [main] org.apache.hadoop.mapred.Merger: Down to the last merge-pass, with 2 segments left of total size: 265119345 bytes
2014-06-27 09:55:12,279 INFO [main] org.apache.zookeeper.ZooKeeper: Initiating client connection, connectString=localhost:2181 sessionTimeout=90000 watcher=hconnection-0x65afdbbb, quorum=localhost:2181, baseZNode=/hbase
2014-06-27 09:55:12,281 INFO [main] org.apache.hadoop.hbase.zookeeper.RecoverableZooKeeper: Process identifier=hconnection-0x65afdbbb connecting to ZooKeeper ensemble=localhost:2181
2014-06-27 09:55:12,282 INFO [main-SendThread(localhost.localdomain:2181)] org.apache.zookeeper.ClientCnxn: Opening socket connection to server localhost.localdomain/127.0.0.1:2181. Will not attempt to authenticate using SASL (Unable to locate a login configuration)
2014-06-27 09:55:12,283 WARN [main-SendThread(localhost.localdomain:2181)] org.apache.zookeeper.ClientCnxn: Session 0x0 for server null, unexpected error, closing socket connection and attempting reconnect
java.net.ConnectException: Connection refused
    at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
    at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:599)
    at org.apache.zookeeper.ClientCnxnSocketNIO.doTransport(ClientCnxnSocketNIO.java:350)
    at org.apache.zookeeper.ClientCnxn$SendThread.run(ClientCnxn.java:1068)
2014-06-27 09:55:12,384 WARN [main] org.apache.hadoop.hbase.zookeeper.RecoverableZooKeeper: Possibly transient ZooKeeper, quorum=localhost:2181, exception=org.apache.zookeeper.KeeperException$ConnectionLossException: KeeperErrorCode = ConnectionLoss for /hbase/hbaseid
2014-06-27 09:55:12,384 INFO [main] org.apache.hadoop.hbase.util.RetryCounter: Sleeping 1000ms before retry #0...
2014-06-27 09:55:13,385 INFO [main-SendThread(localhost.localdomain:2181)] org.apache.zookeeper.ClientCnxn: Opening socket connection to server localhost.localdomain/127.0.0.1:2181. Will not attempt to authenticate using SASL (Unable to locate a login configuration)
2014-06-27 09:55:13,385 WARN [main-SendThread(localhost.localdomain:2181)] org.apache.zookeeper.ClientCnxn: Session 0x0 for server null, unexpected error, closing 
***
org.apache.hadoop.hbase.zookeeper.RecoverableZooKeeper: Possibly transient ZooKeeper, quorum=localhost:2181, exception=org.apache.zookeeper.KeeperException$ConnectionLossException: KeeperErrorCode = ConnectionLoss for /hbase/hbaseid
2014-06-27 09:55:13,486 ERROR [main] org.apache.hadoop.hbase.zookeeper.RecoverableZooKeeper: ZooKeeper exists failed after 1 attempts
2014-06-27 09:55:13,486 WARN [main] org.apache.hadoop.hbase.zookeeper.ZKUtil: hconnection-0x65afdbbb, quorum=localhost:2181, baseZNode=/hbase Unable to set watcher on znode (/hbase/hbaseid)
org.apache.zookeeper.KeeperException$ConnectionLossException: KeeperErrorCode = ConnectionLoss for /hbase/hbaseid

Estoy bastante seguro de que está configurado correctamente, aquí está la parte relevante de mi hbase-site.xml.

<property>
  <name>hbase.zookeeper.property.clientPort</name>
  <value>5181</value>
  <description>Property from ZooKeeper's config zoo.cfg.
    The port at which the clients will connect.
    </description>
</property>
<property>
  <name>zookeeper.session.timeout</name>
  <value>10000</value>
  <description></description>
</property>
<property>
  <name>hbase.client.retries.number</name>
  <value>10</value>
  <description></description>
</property>
<property>
  <name>hbase.zookeeper.quorum</name>
  <value>hdev01,hdev02,hdev03</value>
  <description></description>
</property>

Hasta donde puedo decir, hdev03 es el único servidor que tiene algún problema con esto. Establecer todos los puertos relevantes no me muestra nada extraño.