gcsfuse

README

gcsfuse is a user-space file system for interacting with Google Cloud Storage.

Current status

Please treat gcsfuse as beta-quality software. Use it for whatever you like, but be aware that bugs may lurk, and that we reserve the right to make small backwards-incompatible changes.

The careful user should be sure to read semantics.md for information on how gcsfuse maps file system operations to GCS operations, and especially on surprising behaviors. The list of open issues may also be of interest.

Installing

See installing.md for full installation instructions. The summary is that if you already have Go, fuse, and Git installed, you need only run:

go get github.com/googlecloudplatform/gcsfuse

This will fetch the gcsfuse sources, build them, and install a binary named gcsfuse to $GOPATH/bin. If you ever need to update to the latest version of gcsfuse, you can do so with:

go get -u github.com/googlecloudplatform/gcsfuse

Mounting

Prerequisites

Before invoking gcsfuse, you must have a GCS bucket that you want to mount. If your bucket doesn't yet exist, create one using the Google Developers Console.

In order to be permitted by GCS to access your bucket, gcsfuse requires appropriate credentials in the form of a service account. Follow the instructions here to create a service account, generate a private key, and download a JSON file containing the private key. Place the JSON file on the machine that will be mounting the bucket.

Invoking gcsfuse

To mount a bucket using gcsfuse, invoke it like this:

gcsfuse my-bucket /path/to/mount/point

The directory onto which you are mounting the file system (/path/to/mount/point in the above example) must already exist.

The gcsfuse tool will run until the file system is unmounted. By default little is printed, but you can use the --fuse.debug flag to turn on debugging output to stderr. If the tool should happen to crash, crash logs will also be written to stderr.

If you are mounting a bucket that was populated with objects by some other means besides gcsfuse, you may be interested in the --implicit_dirs flag. See the notes in semantics.md for more information.

See mounting.md for more detail, including notes on running as a daemon and fstab compatiblity.

Performance

GCS round trips

By default, gcsfuse uses two forms of caching to save round trips to GCS, at the cost of consistency guarantees. These caching behaviors can be controlled with the flags --stat_cache_ttl and --type_cache_ttl. See semantics.md for more information.

Downloading file contents

Behind the scenes, when a newly-opened file is first read or modified, gcsfuse downloads the entire backing object's contents from GCS. (Unless it is a newly-created file, of course.) The contents are stored in a local temporary file whose location is controlled by the flag --temp_dir and whose size is controlled with --temp_dir_limit, which is used to serve reads and modifications. Later, when the file is closed or fsync'd, gcsfuse writes the contents of the local file back to GCS as a new object generation.

The consequence of this is that gcsfuse is relatively efficient when reading or writing entire large files, but will not be particularly fast for small numbers of random reads or writes within larger files. Performance when copying large files into GCS is comparable to gsutil (see issue #22 for testing notes). There is some overhead due to the staging of data in a local temporary file, as discussed above.

Other performance issues

If you notice otherwise unreasonable performance, please file an issue.

# Support

gcsfuse is open source software, released under the Apache license. It is distributed as-is, without warranties or conditions of any kind. Best effort community support is available on StackExchange with the google-cloud-platform and google-cloud-storage tags. Please be sure to look at previous questions and answers before asking a new one. For bugs and feature requests, please file an issue.