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EROFS - Wikipedia

From Wikipedia, the free encyclopedia

EROFS
Limits
Developer(s)	Huawei originally, Alibaba Cloud, Bytedance, Coolpad, Google, OPPO
Full name	Enhanced Read-Only File System
Introduced	November 24, 2019 (2019-11-24) with Linux 5.4
Max volume size	16 TiB
Max file size	4 GiB (compact) 16 EiB (extended, also limited by volume size)^[1]
Max no. of files	Depends on volume size
Max filename length	255 bytes
Features
Dates recorded	File change time (extended only)^[1]
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)^[1]
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]

Features

The file system has two different inode on-disk layouts. One is compact, and the other is extended.^[1]

Little-endian on-disk design^[1]
32-bit block addressing, which currently limits the total possible capacity of an EROFS filesystem to 16 TiB of 4 KiB block size.^[1]
Metadata and data can be mixed by design for on-disk flexibility together with tail-packing inline data technology^[1]
Support POSIX attributes and permissions, extended file attributes and ACL^[1]
Fixed-size output transparent compression with LZ4, MicroLZMA (since Linux 5.16^[10]) and/or DEFLATE (since Linux 6.6^[11]) for relative higher compression ratios^[1]
In-place decompression for higher sequential read ^[12]^[13]
Big pcluster feature allowing up to 1 MiB big pclusters for better compression ratios since Linux 5.13.^[14]^[15]
Direct I/O, Direct Access (DAX) support, chunk-based data de-duplication for uncompressed files since Linux 5.15.^[1]^[16]
Multiple device support for multiple layer container images since Linux 5.16.^[1]
Ztailpacking support since Linux 5.17.^[17]
File-based Fscache backend support since Linux 5.19 with "on-demand mode".^[18]^[19]
Rolling-hash deduplicated data compression and fragment support since Linux 6.1. ^[1]

References

^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m 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.
^ Michael Larabel. "EROFS File-System Adding LZMA Compression Support Via New MicroLZMA". Phoronix. Retrieved 2022-01-10.
^ Michael Larabel. "EROFS File-System Adding DEFLATE Compression Support". Phoronix. Retrieved 2023-09-03.
^ "staging: erofs: introduce LZ4 decompression inplace". Retrieved 2020-12-03.
^ "staging: erofs: integrate decompression inplace". Retrieved 2020-12-03.
^ Michael Larabel. "EROFS Sends In "Big Pcluster" Support For Linux 5.13, Other Improvements". Phoronix. Retrieved 2021-07-11.
^ "erofs: add big pcluster compression support". Retrieved 2021-07-11.
^ Michael Larabel. "XFS & EROFS File-Systems Have Big Changes For Linux 5.15". Phoronix. Retrieved 2021-11-02.
^ "EROFS-Utils 1.5 Released With ZTailPacking, FSCK Extraction". Retrieved 2022-08-04.
^ Jonathan Corbet. "5.19 Merge window, part 1". Retrieved 2022-08-04.
^ Marius Nestor (31 July 2022). "Linux Kernel 5.19 Officially Released, Linus Torvalds Teases Linux 6.0 as Next Kernel Series". Retrieved 2022-08-04.

External links

Official website
EROFS Linux kernel repo - git.kernel.org
erofs-utils - git.kernel.org
ATC '19 - EROFS: A Compression-friendly Readonly File System for Resource-scarce Devices
An introduction to EROFS - LWN.net
EROFS, an Introduction and our Smartphone Practice on YouTube
EROFS vs. SquashFS: A Gentle Benchmark - blog.sigma-star.at
Finding the Best Block Filesystem for Your Embedded Linux System - Michael Opdenacker, Bootlin on YouTube

File systems

Disk and
non-rotating

ADFS
AdvFS
Amiga FFS
Amiga OFS
APFS
AthFS
bcachefs
BFS
- Be File System
- Boot File System
- Byte File System (z/VM)
Btrfs
CVFS
CXFS
DFS
EFS
- Encrypting File System
- Extent File System
Episode
ext
- ext2
- ext3
- ext3cow
- ext4
FAT
- exFAT
Files-11
Fossil
GPFS
HAMMER
- HAMMER2
HFS (Classic Mac OS)
HFS (MVS)
HFS+
HPFS
HTFS
JFS
LFS
MFS
- Macintosh File System
- TiVo Media File System
MINIX
NetWare File System
Next3
NILFS
- NILFS2
NSS
NTFS
OneFS
OpenZFS
PFS
QFS
QNX4FS
ReFS
ReiserFS
- Reiser4
Reliance
Reliance Nitro
RFS
SFS
- Shared File System (VM)
- Smart File System
SNFS
Soup (Apple)
Tux3
UBIFS
UFS/UFS2
- soft updates
- WAPBL
VxFS
WAFL
Xiafs
XFS
Xsan
zFS (z/OS)
ZFS (Sun)

Optical disc

Flash memory and SSD

host-side wear leveling	CHFS JFFS JFFS2 LogFS NILFS NILFS2 YAFFS UBIFS

Distributed parallel

NAS

Specialized

Aufs AXFS Boot File System CDfs Compact Disc File System cramfs Davfs2 EROFS FTPFS FUSE Lnfs LTFS NOVA MVFS SquashFS UMSDOS OverlayFS UnionFS
Pseudo	configfs devfs debugfs kernfs procfs specfs sysfs tmpfs WinFS
Encrypted	eCryptfs EncFS EFS Rubberhose SSHFS ZFS

Types

Features

Case preservation Copy-on-write Data deduplication Data scrubbing Execute in place Extent File attribute Extended file attributes File change log Fork Links Hard Symbolic
Access control	Access-control list Filesystem-level encryption Permissions Modes Sticky bit