# Extent File System

> extent-based file system used in IRIX releases prior to version 5.3

**Wikidata**: [Q4038462](https://www.wikidata.org/wiki/Q4038462)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Extent_File_System)  
**Source**: https://4ort.xyz/entity/extent-file-system

## Summary  
The Extent File System (EFS) is an extent-based file system developed by Silicon Graphics for use in IRIX operating systems prior to version 5.3. It was later replaced by XFS.

## Key Facts  
- Developer: Silicon Graphics  
- Used in: IRIX operating system releases before version 5.3  
- Replaced by: XFS  
- Aliases: EFS, EFS (IRIX)  
- Instance of: File system  
- Source code repository: http://bxr.su/n/sys/fs/efs/  
- Described at URL: https://www.aeschi.eu/efs/  
- Freebase ID: /m/03031x  
- Wikipedia languages: English, Norwegian, Portuguese, Russian  

## FAQs  
### Q: What is the Extent File System (EFS)?  
A: EFS is an extent-based file system created by Silicon Graphics for early versions of the IRIX operating system. It organizes data using extents to improve storage efficiency and access performance.

### Q: Which operating system used EFS?  
A: EFS was used in IRIX, specifically in versions prior to IRIX 5.3.

### Q: What replaced the Extent File System?  
A: EFS was replaced by XFS, another file system developed by Silicon Graphics with improved scalability and features.

## Why It Matters  
The Extent File System represents an important step in the evolution of file systems tailored for high-performance computing environments. Developed during the era of Silicon Graphics workstations, EFS introduced extent-based allocation, which reduced fragmentation and improved disk I/O performance compared to traditional block-based systems. Although superseded by more advanced systems like XFS, EFS played a foundational role in shaping modern file system design principles within Unix-like operating systems. Its legacy lies in bridging early filesystem limitations with scalable solutions suited for graphics and scientific computing applications.

## Notable For  
- Being one of the first extent-based file systems integrated into a commercial Unix variant  
- Serving as the default file system in pre-5.3 versions of IRIX  
- Introducing efficient space management through extent allocation techniques  
- Acting as the direct predecessor to XFS, a widely adopted enterprise-grade file system  

## Body  
### Overview  
The Extent File System (EFS) is a local file system designed for the IRIX operating system, originally developed by Silicon Graphics. It uses extent-based allocation to manage file data efficiently on disk.

### Technical Design  
Extent-based allocation allows EFS to store files as contiguous blocks when possible, reducing metadata overhead and improving read/write speeds. Files are represented internally using extents—consecutive sequences of disk blocks—which helps minimize fragmentation over time.

### Operating System Support  
EFS was included as the standard file system in IRIX up until version 5.3. With the release of IRIX 5.3, Silicon Graphics transitioned to XFS, offering better support for large volumes and files, journaling capabilities, and enhanced performance.

### Legacy and Replacement  
XFS succeeded EFS due to its superior scalability and feature set, including support for metadata journaling and very large storage configurations. Despite being deprecated, EFS remains historically significant in the development timeline of Silicon Graphics' software stack.

### Availability  
Documentation and historical information about EFS can be found online, including archived resources such as https://www.aeschi.eu/efs/. The original source code is accessible via cross-reference tools at http://bxr.su/n/sys/fs/efs/.

## References

1. [Source](http://bxr.su/n/sys/fs/efs/efs.h)