It contains 5 software daemons: 1. Name Node 2. Secondary Name Node 3. Data Node 4. Job Tractor 5. Task Tractor 1.Name Node: It is a master node.It contains metadata. i.e it gives the information about the physical locations of the blocks. i.e in contains the blocks information,but not data. 2.Secondary Name Node: when ever the name node goes down the secondary name node comes into picture and does the house keeping activities. i.e the persistent data will be maintain in two files. 1. NamesSpaceImage 2. EditLog 3.Data Node: It is a slave node,it stores the data in the form of blocks. 4.Job Tracker: It is a software daemon resides in name node. it is mainly responsible for distributing,monitoring and rescheduling the map reduce tasks to task trackers. 5. Task Tracker:It is also a software daemon,which will does the execution of the map reduce tasks.