FUSE-based POSIX API
- Advanced configuration
- Assumptions and limitations
- Performance considerations
- Configuration Parameters For Alluxio-FUSE
Alluxio-FUSE is a feature that allows mounting the distributed Alluxio File System as a standard
file system on most flavors of Unix. By using this feature, standard bash tools (for example,
mkdir) will have basic access to the distributed Alluxio data store. More importantly,
with FUSE, an application written in any language like C, C++, Python, Ruby, Perl, or Java, can
interact with Alluxio by using standard POSIX APIs like
open, write, read, without any Alluxio
client integration or set up.
Alluxio-FUSE is based on the project Filesystem in Userspace (FUSE), and most basic file system operations are supported. However, given the intrinsic characteristics of Alluxio, like its write-once/read-many-times file data model, the mounted file system will not have full POSIX semantics and will have specific limitations. Please read the section of limitations for details.
- JDK 1.8 or newer
- libfuse 2.9.3 or newer (2.8.3 has been reported to also work - with some warnings) for Linux
- osxfuse 3.7.1 or newer for MacOS
After having properly configured and started the Alluxio cluster, and from the node where you wish
to mount Alluxio, point a shell to your
$ALLUXIO_HOME and run:
integration/fuse/bin/alluxio-fuse mount mount_point [alluxio_path]
This will spawn a background user-space java process (alluxio-fuse) that will mount the Alluxio path
alluxio_path to the local file system on the specified
For example, the following command will mount the Alluxio path
/people to the folder
in the local file system.
integration/fuse/bin/alluxio-fuse mount /mnt/people /people Starting alluxio-fuse on local host. Alluxio-fuse mounted at /mnt/people. See /lib/alluxio/logs/fuse.log for logs
alluxio_path is not given, Alluxio-FUSE defaults it to root (
/). Note that the
mount_point must be an existing and empty path in your local file system hierarchy and that the
user that runs the
alluxio-fuse.sh script must own the mount point and have read and write
permissions on it. You can mount Alluxio to multiple mount points. All of these alluxio-fuse
processes share the same log output at
$ALLUXIO_HOME\logs\fuse.log, which is useful for
troubleshooting when errors happen on operations under the mounting point.
To umount a previously mounted Alluxio-FUSE file sytem, on the node where the file system is
mounted, point a shell to your
$ALLUXIO_HOME and run:
integration/fuse/bin/alluxio-fuse umount mount_point
This unmounts the file system at the mounting point and stops the corresponding alluxio-fuse process. For example,
integration/fuse/bin/alluxio-fuse umount /mnt/people Unmount fuse at /mnt/people (PID:97626).
Check the Alluxio-FUSE mounting status
To list the mounting points, on the node where the file system is mounted, point a shell to your
$ALLUXIO_HOME and run:
This outputs the
pid, mount_point, alluxio_path of all the running alluxio-fuse processes.
For example, the output will be like:
pid mount_point alluxio_path 80846 /mnt/people /people 80847 /mnt/sales /sales
Configure Alluxio client options
Alluxio-FUSE is based on the standard Java client API
alluxio-core-client-fs to perform its
operations. You might want to customize the behaviour of the Alluxio client used by Alluxio-FUSE the
same way you would for any other client application.
One possibility, for example, is to edit
$ALLUXIO_HOME/conf/alluxio-site.properties and set your
specific Alluxio client options. Note that these changes should be before Alluxio-FUSE starts.
Assumptions and limitations
Currently, most basic file system operations are supported. However, due to Alluxio implicit characteristics, please be aware that:
- Files can be written only once, only sequentially, and never be modified. That means overriding a
file is not allowed, and an explicit combination of delete and then create is needed. For example,
cpcommand will fail when the destination file exists.
- Alluxio does not have hard-link and soft-link concepts, so the commands like
lnare not supported, neither the hardlinks number is displayed in
- The user and group are mapped to the Unix user and group only when Alluxio Fuse is configured to use
shell user group translation service, by setting
chgrpare no-ops, and
llwill return the user and group of the user who started the alluxio-fuse process. The translation service does not change the actual file permission when running
Due to the conjunct use of FUSE and JNR, the performance of the mounted file system is expected to be worse than what you would see by using the Alluxio Java client directly.
Most of the overheads come from the fact that there are several memory copies going on for each call
write operations, and that FUSE caps the maximum granularity of writes to 128KB. This
could be probably improved by a large extent by leveraging the FUSE cache write-backs feature
introduced in kernel 3.15 (supported by libfuse 3.x userspace libs but not supported in jnr-fuse yet).
Configuration Parameters For Alluxio-FUSE
These are the configuration parameters for Alluxio-FUSE.
|alluxio.fuse.maxwrite.bytes||131072||The desired granularity of FUSE write upcalls in bytes. Note that 128K is currently an upper bound imposed by the linux kernel.|
|alluxio.fuse.debug.enabled||false||Enable FUSE debug output. This output will be redirected in a `fuse.out` log file inside `alluxio.logs.dir`.|
|alluxio.fuse.cachedpaths.max||500||Defines the size of the internal Alluxio-FUSE cache that maintains the most frequently used translations between local file system paths and Alluxio file URIs.|
|alluxio.fuse.fs.name||alluxio-fuse||Descriptive name used by FUSE to mount the file system.|
This project uses jnr-fuse for FUSE on Java.