Colossus is Google’s proprietary, exabyte-scale distributed file system and the direct successor to the original Google File System (GFS). [1] (https://en.wikipedia.org/wiki/Google_File_System), [2] (https://abhishekkumar2718.github.io/programming/2020-03-15-google-file-system.html), [3] (https://siliconangle.com/2021/04/19/google-shares-technical-overview-exabyte-scale-colossus-file-system/)
Core Purpose & Scale
• Underpinning Infrastructure: It serves as the core storage backbone for Google's internal services (like YouTube, Gmail, and Google Search) and Google Cloud offerings (like Cloud Storage, BigQuery, and Cloud SQL). [1] (https://cloud.google.com/blog/products/storage-data-transfer/a-peek-behind-colossus-googles-file-system), [2] (https://www.infoq.com/news/2021/04/google-colossus/), [3] (https://abhishekkumar2718.github.io/programming/2020-03-15-google-file-system.html)
• Real-Time & Batch Workloads: While GFS was built mainly for batch processing, Colossus is architected to handle both low-latency, real-time services and heavy batch workloads simultaneously. [1] (https://research.google.com/pubs/archive/44877.pdf), [2] (https://abhishekkumar2718.github.io/programming/2020-03-15-google-file-system.html)
• Borg Integration: Unlike GFS—which ran on dedicated master machines—Colossus runs natively inside Google's Borg cluster management infrastructure. [1] (https://news.ycombinator.com/item?id=39756262), [2] (https://cloud.google.com/blog/products/storage-data-transfer/a-peek-behind-colossus-googles-file-system)
Key Architectural Components
Colossus breaks down its tasks into specialized distributed pieces:
• Curators: The control plane metadata servers that handle file creation, deletion, and directory operations. They scale horizontally and store metadata inside Google's Bigtable, allowing the system to scale over 100 times larger than legacy GFS clusters. [1] (https://cloud.google.com/blog/products/storage-data-transfer/how-colossus-optimizes-data-placement-for-performance), [2] (https://techfieldday.com/video/the-latest-in-high-performance-storage-rapid-on-colossus-with-google-cloud/), [3] (https://www.scribd.com/document/829043634/Colossus-Google-s-File-System), [4] (https://www.infoq.com/news/2021/04/google-colossus/)
• Custodians: Maintenance workers that handle data durability, replication, disk space balancing, garbage collection, and RAID reconstruction. [1] (https://www.infoq.com/news/2021/04/google-colossus/), [2] (https://cloud.google.com/blog/products/storage-data-transfer/how-colossus-optimizes-data-placement-for-performance), [3] (https://techfieldday.com/video/the-latest-in-high-performance-storage-rapid-on-colossus-with-google-cloud/)
• "D" File Servers: A massive fleet of network-attached disk servers (HDDs and SSDs) that store the actual raw bytes of files. [1] (https://techfieldday.com/video/the-latest-in-high-performance-storage-rapid-on-colossus-with-google-cloud/), [2] (https://www.infoq.com/news/2021/04/google-colossus/), [3] (https://cloud.google.com/blog/products/storage-data-transfer/how-colossus-optimizes-data-placement-for-performance)
• Colossus Client Library: The entry point for applications; it talks to Curators to resolve file handles and metadata, then communicates directly with D servers for data transfer (minimizing physical network hops). [1] (https://www.storagenewsletter.com/2025/04/14/google-cloud-colossus-secret-ingredient-in-rapid-storages-high-performance/), [2] (https://www.infoq.com/news/2021/04/google-colossus/), [3] (https://techfieldday.com/video/the-latest-in-high-performance-storage-rapid-on-colossus-with-google-cloud/)
Would you like to explore how Colossus compares to other distributed file systems like HDFS or how it integrates with Google Cloud Storage?