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.

swillner / ramcachefs