⚖️ Features and Comparison

Note that it’s just an incomplete list for the qualitative evaluation. The overall purpose of this is to show EROFS benefits compared to other in-kernel approaches when making technical decisions.

Feature (as of Linux 6.17)	EROFS	EXT4	SquashFS
Minimal block size	512 B [1]	1 KiB	Unaligned[2]
Inode size	32/64 B	128/256 B	Varied [3]
Limitation of total UIDs/GIDs	Unlimited	Unlimited	65536 [4]
Pre-1970 / ns timestamps	Yes	Yes	No
Filesystem UUID	Yes	Yes	No
Filesystem label (Volume label)	Yes	Yes	No
Inline data	Yes (Inline tail)	Yes	No
Data compression	Yes [5]	No	Yes
Largest compression granularity	1 MiB	N/A	1 MiB
Default compression granularity	1 Block [6]	N/A	128 KiB
Fragments	Yes	N/A	Yes
File-backed mounts	Yes [7]	No	No
Metadata compression	Yes [8]	N/A	Yes
Multiple compression algorithms	Per-file	N/A	No
Data deduplication	Extent-based	No? [9]	File-based
Extended attribute support	Yes	Yes	Yes
External data (multi-devices)	Yes	No	No
POSIX.1e ACL support	Yes	Yes	No
Direct I/O support [10]	Yes	Yes	No
FIEMAP support	Yes	Yes	No
SEEK_{DATA,HOLE} support	Yes	Yes	No
FSDAX support	Yes	Yes	No
Large folio support	Yes [11]	Yes [12]	No
Hardware acceleration support	Yes [13]	No	No

---

[1]

512-byte blocks can be used for tarball data reference.

[2]

It means a fixed minimal filesystem I/O size which SquashFS doesn’t have. Instead, SquashFS has its own “block size”: its compressed files are split up in fixed-size blocks. See Squashfs Binary Format/About.

[3]

SquashFS has different on-disk inodes for each type of varying contents and size. See Squashfs Binary Format/Inode Table.

[4]

SquashFS allows 32-bit UIDs/GIDs, but only among 2¹⁶ unique values. See Squashfs Binary Format/Inode Table.

[5]

Data compression is an optional feature of the EROFS filesystem. Currently, the supported compression algorithms include LZ4, MicroLZMA (since Linux 5.16), DEFLATE (since Linux 6.6 LTS) and Zstandard (since Linux 6.10).

[6]

The default block size of EROFS is 4 KiB on x86 and x86-64.

[7]

EROFS has supported EROFS over fscache (since Linux 5.19, deprecated in Linux 6.12) and file-backed mounts (since Linux 6.12) to avoid unnecessary loop devices.

[8]

EROFS metadata is designed to be directly accessible from block devices without decoding, or deserialization, as these can lead to I/O amplification and additional runtime latency in performance-critical scenarios. Nevertheless, optional metadata compression has been supported since Linux 6.17 to minimize filesystem images.

[9]

Strictly speaking, EXT4 has a feature named “shared_blocks”, which will prevent applications from writing to the filesystem.

[10]

For example, direct I/O can be used for loop devices backed by unencoded files on the EROFS filesystem to avoid double caching. Direct I/O on encoded files is almost useless since it should not do ANY caching and thus will kill the overall performance.

[11]

EROFS has supported large folios for uncompressed files (since Linux 6.2) and compressed files (since Linux 6.11).

[12]

EXT4 supports large folios since Linux 6.16.

[13]

EROFS has supported Intel QuickAssist Technology to accelerate DEFLATE algorithm since Linux 6.16.