I'm running Hadoop 1.1.2 on a cluster with 10+ machines. I would like to nicely scale up and down, both for HDFS and MapReduce. By "nicely", I mean that I require that data not be lost (allow HDFS nodes to decomission), and nodes running a task finish before shutting down.
I've noticed the datanode process dies once decomissioning is done, which is good. This is what I do to remove a node:
- Add node to mapred.exclude
- Add node to hdfs.exclude
$ hadoop mradmin -refreshNodes
$ hadoop dfsadmin -refreshNodes
$ hadoop-daemon.sh stop tasktracker
To add the node back in (assuming it was removed like above), this is what I'm doing.
- Remove from mapred.exclude
- Remove from hdfs.exclude
$ hadoop mradmin -refreshNodes
$ hadoop dfsadmin -refreshNodes
$ hadoop-daemon.sh start tasktracker
$ hadoop-daemon.sh start datanode
Is this the correct way to scale up and down "nicely"? When scaling down, I'm noticing job-duration rises sharply for certain unlucky jobs (since the tasks they had running on the removed node need to be re-scheduled).