S3FS cache on cloud environment

By default, S3FS cache may be enabled in preconfigured Linux images on cloud environment. If the /eodata repository is mounted through s3fs, you can check the cache configuration in /etc/fstab.

The entry may look similar to this:

#s3fs#eodata /eodata fuse passwd_file=/root/.passwd-s3fs,_netdev,allow_other,use_path_request_style,uid=0,umask=0222,mp_umask=0222,gid=0,stat_cache_expire=20,url=https://s3.r1.cloud.eumetsat.int,use_cache=1,max_stat_cache_size=60000,list_object_max_keys=10000 0 0

In this example, the use_cache parameter points to the cache directory /1. The value 1 is interpreted as a directory name at the beginning of the filesystem hierarchy.

The s3fs documentation describes this option as follows:

-o use_cache (default="" which means disabled)
local folder to use for local file cache.

Directory /1 is therefore used as a local cache destination for products from the EODATA repository during processing or downloading.

Clearing the cache

If you encounter problems with displaying folders or files inside /eodata, for example errors such as No such file or directory, empty the /1 folder.

Before doing this, make sure that no process is currently using files from /eodata or from the cache directory.

Preventing disk space problems

If the cache directory occupies too much disk space, you may have problems remounting the /eodata repository.

A common error message is:

clnt_create: RPC: Timed out
s3fs: There is no enough disk space for used as cache(or temporary) directory by s3fs.

To reduce the risk of this situation, consider setting the ensure_diskfree parameter in the s3fs mount configuration.

The s3fs documentation describes this option as follows:

-o ensure_diskfree(default 0)

This option defines the minimum amount of free disk space that should remain available on the disk used for the s3fs cache. s3fs creates files for downloading, uploading, and caching. If the available free space is smaller than the configured value, s3fs avoids using additional disk space where possible, at the cost of lower performance.

Example with ensure_diskfree

The following example keeps the same structure as the previous /etc/fstab entry, but adds ensure_diskfree.

#s3fs#eodata /eodata fuse passwd_file=/root/.passwd-s3fs,_netdev,allow_other,use_path_request_style,uid=0,umask=0222,mp_umask=0222,gid=0,stat_cache_expire=20,url=https://s3.r1.cloud.eumetsat.int,use_cache=1,ensure_diskfree=1024,max_stat_cache_size=60000,list_object_max_keys=10000 0 0

In this example, ensure_diskfree=1024 tells s3fs to avoid using the cache disk when less than 1024 MB of free space remains.

Adjust this value to match the size of your disk and the expected workload. After editing /etc/fstab, reload systemd and remount the resource if needed:

sudo systemctl daemon-reload
sudo mount /eodata