翻译《Pro Hadoop 》Jason Venner著，部分章节
JobTracker & TaskTracker
The framework provides two processes that handle the management of MapReduce jobs:
• TaskTracker manages the execution of individual map and reduce tasks on a compute
node in the cluster.
• JobTracker accepts job submissions, provides job monitoring and control, and manages
the distribution of tasks to the TaskTracker nodes.
MapReduce job的管理有两种：TaskTracker 和JobTracker
TaskTracker ——map和reduce任务的执行
JobTracker ——map和reduce任务的接受，监控和管理TaskTracker 的分布式任务
1个节点上有1个JobTacker，但有1个或以上的TaskTracker，
NameNode & DataNode
HDFS services are provided by two processes:HDFS服务提供2个进程
• NameNode handles management of the file system metadata, and provides management
and control services.
• DataNode provides block storage and retrieval services.
NameNode提供管理，文件系统元数据，管理和监控服务，DataNode用于数据存储和检索服务