Filesystems

This page contains basic information about filesystems (file systems) and partitions. A filesystem is “how data is written in a partition of the storage device”. Windows, macOS, and Linux use different default filesystems, and not all filesystems work equally well across operating systems.

OpenWrt is a Linux-based operating system and thus typically works best with filesystems native to Linux. However it can also read/write data with many filesystems, albeit sometimes slower or less reliable than with native Linux filesystems. In case you wonder, the reason for this reduced performance is patents and other ways to impede the adoption of Microsoft or Apple filesystems by other parties.

Installing these additional filesystems in OpenWrt is commonly for file sharing using USB 3.0 storage and Samba.

To see what filesystems can be read currently, enter cat /proc/filesystems.

A full list of filesystems available in OpenWrt can be obtained by writing
opkg update && opkg list | grep kmod-fs

The tools for the filesystem of your choosing can be found by writing
opkg list | grep FILESYSTEM_NAME

OpenWrt has drivers and filesystem tools available for ext2/3/4, f2fs, btrfs, and many other filesystems supported by Linux.

The two most common Linux filesystems are ext4 and f2fs, with btrfs growing in popularity:

• ext4 is well suited for HDDs and SSDs (using TRIM) and is the default filesystem of most desktop Linux distributions.
• f2fs is well suited for flash (SSDs or USB thumbdrives). The format can be incompatible between kernel versions, requiring some time for “fsck” to upgrade the filesystem.
• btrfs is the default filesystem for more cutting-edge Linux distributions. It is considered the sucessor to ext4, with the author stating “there will be no ext5”. It has some more advanced features such as checksumming.

This command will download the tools needed to create and fix ext4 (and older versions)
opkg install e2fsprogs

If in the list of supported filesystems in your device you don't see ext4, you must install also the driver itself
opkg install kmod-fs-ext4

This command will download the tools needed to create and fix f2fs
opkg install f2fs-tools

If in the list of supported filesystems in your device you don't see f2fs, you must install also the driver itself
opkg install kmod-fs-f2fs

This command will download the tools needed to create and fix btrfs
opkg install btrfs-progs

If in the list of supported filesystems in your device you don't see btrfs, you must install also the driver itself
opkg install kmod-fs-btrfs

The two most common filesystems used by Windows are NTFS and exFAT as described below.

NTFS is the proprietary file system used in Windows. Two drivers are available with read/write support in Linux, ntfs-3g, and with kernel 5.15 onward the new in-kernel driver ntfs3. See Writable NTFS for important information on mounting and features.

Download and install the NTFS3 driver
opkg install kmod-fs-ntfs3

In Apple land you have HFS, HFS+ and APFS. There is a driver available for HFS and HFS+ but it has low performance and does not support all features. APFS was introduced in 2017 but there is currently no support for it in OpenWrt (nor in Linux).

This command will download the tools needed to create and fix HFS and HFS+
opkg install hfsfsck

If in the list of supported filesystems in your device you don't see hfs and hfsplus, you must install also the drivers
opkg install kmod-fs-hfs kmod-fs-hfsplus

FAT32 was a common multiplatform file system. It can be read/write by Windows, macOS, Linux, and any other device you might have (smartTV, tablets, car audio with usb, etc). Its has two major drawbacks given its age: it cannot store files larger than 3.9 GB, and it lacks journaling support, meaning it's also prone to corruption if the device is disconnected while writing. This can lead to data loss if the device is written again without running a filesystem check.

This command will download the tools needed to create and fix FAT32 (and older versions)
opkg install dosfstools (The dosfstools package includes the mkfs.fat and fsck.fat utilities, which respectively make and check MS-DOS FAT filesystems.)

If in the list of supported filesystems in your device you don't see vfat, you must install also the driver itself
opkg install kmod-fs-vfat

Some filesystems, like FAT32, may need additional Native Language Support (NLS) packages (codepages / charsets) to handle the filenames. If your mount fails, look in dmesg - a message like
FAT: codepage cp437 not found
means that you need NLS codepage 437, and a message like
FAT: IO charset iso8859-1 not found
means that you need NLS ISO 8859-1.

Available NLS packages can be listed by writing opkg update && opkg list “kmod-nls*”. There will be many available, below are a few examples.

exFAT is commonly used by OEMs for external SSDs and SD cards. The downside to this filesystem is the lack of journaling support, which makes breakage during sudden poweroff more likely. exFAT will provide good performance while maintaining compatibility with Windows and macOS.

As of Linux kernel 5.4 there is a new exFAT driver this is available with low overhead. This new driver is quite performant and will max out gigabit LAN at 120 MB/s using USB 3.0 external drives on some targets, as tested on the wrt_ac_series.

This will install the driver to use exFAT and the tool to be able to run check disk if needed:
opkg install kmod-fs-exfat exfat-fsck

Under Windows, exFAT does not support TRIM; but under Linux/OpenWRT, it does.

A partition is a way to split the storage space in more different sections, each using its own independent filesystem.

This can be useful to separate different types of data, for example to keep your expanded firmware separate from the actual data you want to store and share, or data that must be easily accessible from Windows or macOS directly if you disconnect the external drive.

Discussing advanced partitioning is beyond the scope of this article, as OpenWrt uses the same commandline tools used by any other Linux system.

• fdisk tool is used to create/modify partitions on a drive initialized with MBR scheme; since version 2.23 (OpenWRT is on 2.37, as of 2024!), it also supports GPT just fine.
• gdisk tool is used to create/modify partitions on a drive initialized with GPT scheme.