1. Google File System
Dhan V Sagar
CB.EN.P2CSE13007
M.Tech CSE I

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Thousands of queries served per second.
One query reads 100's of MB of data.
One query consumes 10's of billions of CPU cycles.
Google Apps
Dozens of copies of the entire Web…!
DVS
INTRODUCTION
• TRADITIONAL ISSUES
• Need large, distributed, highly fault tolerant file system
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3. DVS
GFS: Architecture
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4. DVS
• Single Master
• Multiple Chunk Servers
• Multiple Clients
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5. Master Server
• Manages metadata
• Performs check pointing and logging of changes to metadata
DVS
• Manages chunk creation, replication, placement
• Garbage Collection
• Periodically communicate with chunkservers (Heart Beat
Message)
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6. Master Server
• Single Point Failure..??
• Shadow Masters
DVS
• Least involvement of master
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7. Chunk
• Files are divided into fixed-size chunks
• Chunk Servers store chunks on local disk as Linux files
• Replication for Reliability
DVS
• Unique 64 bit chunkhandle
• Chunk Size : 64MB - Much larger than typical file system block sizes
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8. Large Chunk Size
• Reduce interaction between client and master
• Reduces network overhead by keeping persistent TCP connection
DVS
• Reduce size of metadata stored on the master
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9. Client
• Control (metadata) requests to master server
• Caches metadata
DVS
• Data requests to chunkservers
• No caching of data
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10. Client Read
• Client sends master:
• read(file name, chunk index)
• chunk ID, chunk version number, locations of replicas
DVS
• Master’s reply:
• Client sends “closest” chunkserver replica:
• read(chunk ID, byte range)
• “Closest” determined by IP address on simple rackbased network topology
• Chunkserver replies with data
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11. DVS
Client Read
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12. DVS
Client Read
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13. DVS
Client Write
1. Application originates the request
2. GFS client translates request and sends it to master
3. Master responds with chunk handle and replica locations
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14. DVS
Client Write
4. Client pushes write data to all locations. Data is stored
in chunkserver’s internal buffers
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15. DVS
Client Write
5. Client sends write command to primary
6. Primary determines serial order for data instances in its buffer and writes the
instances in that order to the chunk
7. Primary sends the serial order to the secondaries and tells them to perform
the write
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16. DVS
Client Write
8. Secondaries respond back to primary
9. Primary responds back to the client
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17. File Deletion
• Master records deletion in its log
• File renamed to hidden name including deletion
timestamp
DVS
• When client deletes file:
• Master scans file namespace in background:
• In-memory metadata erased
• Master scans chunk namespace in background:
• Removes unreferenced chunks from chunkservers
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18. References
DVS
• The Google File System - Sanjay Ghemawat, Howard
Gobioff, and Shun-Tak Leung
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19. DVS
THANK YOU
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