ramcachefs

Userspace in-memory filesystem with on-demand persistance using FUSE (Filesystem in Userspace).

ramcachefs caches a directory in memory and persists changes to the directory and its files back to disk on demand only. Useful for caching directories with lots of read/write operations, e.g. for inefficient I/O processes or to protect SSDs from frequent writes to browser caches.

Features

• No root needed as long as FUSE is enabled on the system (unlike tmpfs)
• Caches the directory and all its files and subdirectories in place (i.e. no path changes for processes accessing the directory)
• Write-back of changes (file changes, type changes, creations, deletions, permissions, and changes to owner) on demand (calling ramcachefs -p <mountpoint>) and optionally automatically after unmount.

Installation

Prerequisites

To build ramcachefs you need the FUSE 3 libraries. On Debian/Ubuntu, just install these using

sudo apt-get install libfuse3-dev

Building

Just build the ramcachefs binary using

make

Usage

Just call the ramcachefs binary and specify the directory to cache as <mountpoint>. By default it forks to the background as a daemon, which can be disabled using the -f option. Stop the caching by unmounting the <mountpoint> (umount <mountpoint) or by terminating the ramcachefs process.

Persist changes done so far back to the underlying directory on disk (or any other filesystem to start with) calling ramcachefs -p <mountpoint>. By default changes are persistet after unmount, which can be disabled using the -o noautopersist option.

Options

usage: ramcachefs [options] <mountpoint>

    -p   --trigger-persist trigger persist
    -h   --help            print help
    -V   --version         print version
    -d   -o debug          enable debug output (implies -f)
    -f                     foreground operation
    -s                     disable multi-threaded operation
    -o clone_fd            use separate fuse device fd for each thread
                           (may improve performance)
    -o max_idle_threads    the maximum number of idle worker threads
                           allowed (default: 10)
    -o allow_other         allow access by all users
    -o allow_root          allow access by root
    -o auto_unmount        auto unmount on process termination
    -o direct_io           always use direct_io (breaks mmap!)
    -o maxinodes=NUMBER    maximum number of inodes (default: '1000000')
    -o noautopersist       do not persist on unmount
    -o prepopulate         read full files at start (prepopulate mmaps)
    -o size=SIZE           size (default: '1G')

Disclaimer

Bugs in filesystems can easily lead to data losses! Use ramcachefs at your own risk. I am using it on a day-to-day basis without any issues so far. Nevertheless, please be careful when using it for crucial data.