Name node

see also Secondary name node

• MOST IMPORATANT FOR CLUSTER!
• in-memory location of every Data block in cluster / rack
• Controlls DataNodes
• FS Ops
• Block Mapping
• Send cordinates to clients where to get the Data blocks and witch Data node
• Name node retrives every 3 secounds heart-bit from Data node
• If Name node not retrives from the Data node heart-bit more then 10 minutes Name node will consedure the Data node as a Dead node and the Name node start to replicate all Data blocks that has on a Dead node to other nodes

• Should have LOT OF RAM, LOT OF MEM, LOT OF POWER

• RAM
  • Edit log
  • fsImage
• FILE
  • fsImage

When proccess of Reboot or Checkpoint the RAM\fsImage marges with Edit log to FILE\fsImage file that makes it to keep presistnece.