EROFS information

EROFS
Developer(s)	Huawei originally, Alibaba Cloud, Bytedance, Coolpad, Google, OPPO
Full name	Enhanced Read-Only File System
Introduced	November 24, 2019 with Linux 5.4
Limits
Max volume size	16 TiB
Max file size	4 GiB (compact); 16 EiB (extended, also limited by volume size);
Max no. of files	Depends on volume size
Max filename length	255 bytes
Features
Dates recorded	File change time (extended only)
Date resolution	1 ns
Attributes	POSIX, Extended file attributes
File system; permissions	POSIX, ACL
Transparent; compression	Yes (LZ4; LZMA since 5.16; DEFLATE since 6.6)
Data deduplication	Yes (extent-based)
Other
Supported; operating systems	Linux

EROFS (Enhanced Read-Only File System) is a lightweight read-only file system initially developed by Huawei, originally for the Linux kernel and now maintained by an open-source community from all over the world.

EROFS aims to form a generic read-only file system solution for various read-only use cases (embedded devices, containers and more) instead of just focusing on storage space saving without considering any side effects of runtime performance.^[1]

For example, it provides a solution to save storage space by using transparent compression as an option for scenarios that need high-performance read-only requirements on their devices with limited hardware resources, e.g. smartphones like Android and IoT operating systems such as HarmonyOS alongside its HarmonyOS NEXT core system iteration.^[2]^[3] All of Huawei's new products shipped with EMUI 9.0.1 or later used EROFS,^[4] and it was promoted as one of the key features of EMUI 9.1.^[5] Oppo, Xiaomi and some Samsung products also use EROFS.^[6]^[7]

Also, it provides a content-addressable chunk-based container image solution together with lazy pulling feature to accelerate container startup speed by using new file-based fscache backend since Linux kernel v5.19.^[8]

The file system was formally merged into the mainline kernel with Linux kernel v5.4.^[9]

^ ^a ^b ^c ^d Gao Xiang. "erofs.html". www.kernel.org. Retrieved 2022-08-04.
^ Michael Larabel (2018-11-19). "There Is Finally A User-Space Utility To Make EROFS Linux File-Systems". Phoronix. Retrieved 2018-12-13.
^ Xiang, Gao (2018-05-31). "erofs: introduce erofs file system". Linux kernel (Mailing list). Retrieved 2018-12-13.
^ Xiang, Gao (2019-07-04). "erofs: promote erofs from staging". Linux kernel (Mailing list). Retrieved 2019-09-03.
^ "EMUI 9.1, the Intelligent Android OS". HUAWEI Global. Huawei Technologies. Retrieved 2022-01-10.
^ "Google's plan to use EROFS on Android". 20 May 2022. Retrieved 2022-08-04.
^ "The Galaxy S23 might be Samsung's first Android device to use EROFS". 2023-02-07. Retrieved 2023-07-22.
^ "The Evolution of the Nydus Image Acceleration". 6 June 2022. Retrieved 2022-08-04.
^ corbet (2019-11-25). "The 5.4 kernel has been released". LWN.net. Retrieved 2019-12-01.

[erofs_documentation-1] Gao Xiang. "erofs.html". www.kernel.org. Retrieved 2022-08-04.

[2] Michael Larabel (2018-11-19). "There Is Finally A User-Space Utility To Make EROFS Linux File-Systems". Phoronix. Retrieved 2018-12-13.

[3] Xiang, Gao (2018-05-31). "erofs: introduce erofs file system". Linux kernel (Mailing list). Retrieved 2018-12-13.

[4] Xiang, Gao (2019-07-04). "erofs: promote erofs from staging". Linux kernel (Mailing list). Retrieved 2019-09-03.

[emui_9.1-5] "EMUI 9.1, the Intelligent Android OS". HUAWEI Global. Huawei Technologies. Retrieved 2022-01-10.

[6] "Google's plan to use EROFS on Android". 20 May 2022. Retrieved 2022-08-04.

[7] "The Galaxy S23 might be Samsung's first Android device to use EROFS". 2023-02-07. Retrieved 2023-07-22.

[8] "The Evolution of the Nydus Image Acceleration". 6 June 2022. Retrieved 2022-08-04.

[9] rbet (2019-11-25). "The 5.4 kernel has been released". LWN.net. Retrieved 2019-12-01.

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