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    Alibaba Cloud Linux:Use EROFS

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    Alibaba Cloud Linux:Use EROFS

    Last Updated:Apr 16, 2025

    Enhanced Read-Only File System (EROFS) is a type of Linux kernel file system designed for high-performance read-only scenarios. Alibaba Cloud Linux operating systems use EROFS in cloud computing scenarios to better meet the distribution and storage requirements of container images, operating system images, software packages, and AI model datasets. This topic describes the common features of EROFS and how to use EROFS.

    Feature comparison

    The following table compares the common features of EROFS, Ext4, and SquashFS file systems.

    Feature

    EROFS

    Ext4

    SquashFS

    Minimum block size

    512 bytes

    1 KiB

    Not aligned

    Inode size

    32 or 64 bytes

    128 or 256 bytes

    Variable based on the file type

    Maximum number of UIDs/GIDs

    Unlimited

    Unlimited

    65,536

    Nanosecond timestamp

    Yes

    Yes

    No

    UUID and volume label

    Supported

    Supported

    Not supported

    Data compression

    Supported

    Not supported

    Supported

    Data deduplication

    Supported

    Not supported

    Not supported

    Mount through files

    Supported

    Not supported

    Not supported

    External data reference

    Supported

    Not supported

    Not supported

    POSIX.1e ACL

    Supported

    Supported

    Not supported

    Direct I/O

    Supported

    Supported

    Not supported

    FSDAX

    Supported

    Supported

    Not supported

    FIEMAP

    Supported

    Supported

    Not supported

    SEEK_{DATA,HOLE} support

    Supported

    Supported

    Not supported

    Create and use file system images

    1. Check whether the erofs-utils package is installed.

      mkfs.erofs -V

      • If a version number of the package is displayed, the package is installed.

      • If no version number of the package is displayed, run the following command to install the erofs-utils package:

        sudo yum install -y erofs-utils

    2. Run the mkfs.erofs command to create a file system image.

      For example, run the following command to create a file system image named foo.erofs from the foo directory:

       mkfs.erofs foo.erofs foo

      The following command output is displayed:

      mkfs.erofs 1.8.4
Build completed.
------
Filesystem UUID: c11813b0-b657-439c-8484-2196703035b7
Filesystem total blocks: 1 (of 4096-byte blocks)
Filesystem total inodes: 1
Filesystem total metadata blocks: 1
Filesystem total deduplicated bytes (of source files): 0

      The following table describes the parameters of the mkfs.erofs command.

      Parameter

      Description

      -zX[,level]

      The compression algorithm (X, which supports only lowercase letters) and the optional compression level (level). LZ4, LZ4HC, LZMA, DEFLATE, and Zstd algorithms are supported. For example, -zlz4hc,12 specifies the LZ4HC algorithm with the compression level set to 12. If no compression algorithm is specified, an uncompressed image is created.

      -C <size>

      The physical cluster size. Unit: bytes. For example, -C 65536 specifies a 64 KiB cluster size. Appropriately increasing the physical cluster size can reduce the image size and improve sequential read performance, but may affect random read performance.

      -T <time>

      The UNIX timestamp for all files.

      -U <UUID>

      The file system UUID.

      -L <label>

      The file system volume label.

    3. Mount the created file system image.

      For example, run the following command to mount the foo.erofs file system image to the /mnt/erofs directory:

      sudo mkdir -p /mnt/erofs
sudo mount -t erofs -o loop foo.erofs /mnt/erofs

      If you no longer use the file system, unmount the file system.

      For example, run the following command unmount the file system mounted at the /mnt/erofs directory:

      sudo umount /mnt/erofs