Distributed File Systems: GFS & HDFS

In GFS/HDFS clusters, metadata lookups route to the NameNode, while high-volume data streams bypass the master entirely through worker pipeline writes:

• Distributed Cluster Node Matrix: Structuring master and worker boundaries:

• Storage Types: Block, File, Object: Contrasting shared filesystems (NFS) with analytical DFS architectures.
• RAID & Durability Basics: Implementing durability at the network layer vs physical disk arrays.
• Write-Ahead Logging (WAL) & Data Durability: Appending WAL logs to HDFS blocks sequentially.

Rack-Aware HDFS Replication Policy (Data Safety Economy)

To shield data against physical switch failures and electrical outages, GFS/HDFS implements a highly specific **Rack-Aware Placement Policy** during write pipelines:

1. Replica 1: Placed on a local DataNode node in the same rack as the client (minimizes initial network latency).
2. Replica 2: Placed on a DataNode located in a *different* remote physical server rack (shields against complete local rack power outages).
3. Replica 3: Placed on a secondary DataNode located in the *same* remote physical server rack as Replica 2 (avoids paying high inter-rack network routing overheads for the third copy).

This optimizes the write pipeline path, balancing local rack writing speed with complete rack-failure survivability.