Courses/Distributed Systems

Distributed Systems

CS3.401

Prof. Kishore Kothapalli•Monsoon 2025-26•4 credits

Revision Notes/Unit 11 — Google File System (GFS)

Unit 11 — Google File System (GFS)

GFS architecture: single master + chunkservers + clients. 64 MB chunks replicated 3× across racks. Leases serialise mutations at a primary replica. Atomic record append. Four consistency states (defined / consistent / undefined / inconsistent). Pipelined data flow vs star control flow. Garbage collection via heartbeats + 3-day hidden retention. Copy-on-write snapshots.

GFS — Architecture, Reads, Writes, Consistency, Recovery

18 min

GFS (2003) is the design Google used to store all of search and Gmail at the time. The radical choices: a **single master** for all metadata (vs many believed this couldn't scale); **64 MB chunks** (vs typical 4 KB block sizes); **failure is the norm** (commodity hardware in racks); **atomic record append** as the primary write operation (vs random in-place writes). The 'inconsistent' / 'undefined' regions in the consistency model are unusual — applications are expected to cope.