CephFS

CephFS (Ceph Filesystem) is a distributed file system that provides high-performance, scalable, and fault-tolerant file storage on top of a Ceph cluster. The cephfs tool allows for the management of a CephFS instance, and many operations are performed using Ceph administrative tools like ceph, mount, rados, and other filesystem tools. However, there are specific subcommands and operations associated with managing CephFS.

Below is a breakdown of cephfs-related subcommands and relevant operations for managing the Ceph filesystem:

General Structure of CephFS Commands

Using the ceph CLI to manage CephFS:

ceph fs <subcommand> [options]

Common cephfs Subcommands

1. Filesystem Management

ceph fs create

Creates a new Ceph filesystem (CephFS) instance.

ceph fs create <filesystem-name> <metadata-pool> <data-pool>

  • Example:

    ceph fs create myfs cephfs_metadata cephfs_data

This creates a new CephFS instance named myfs, with cephfs_metadata as the metadata pool and cephfs_data as the data pool.

ceph fs ls

Lists all the CephFS filesystems available in the Ceph cluster.

  • Example:

This lists all the filesystems configured in the Ceph cluster.

ceph fs rm

Removes a CephFS filesystem from the cluster.

  • Example:

This removes the filesystem myfs from the cluster (use with caution).

2. MDS (Metadata Server) Management

ceph fs status

Displays detailed status information about a CephFS instance, including MDS activity.

  • Example:

This shows the status of the filesystem myfs, including the MDS status and client connections.

ceph fs set

Sets various configuration options for a specific CephFS filesystem.

  • Example:

This sets the maximum number of MDS daemons for the filesystem myfs to 2.

ceph fs dump

Dumps the full configuration of a CephFS instance, including metadata pool, data pool, MDS settings, and placement groups.

  • Example:

This provides a detailed output of the configuration and status of the CephFS instances.

ceph fs mds fail

Manually forces a failover of an MDS daemon to test failover functionality or to replace a non-responsive MDS.

  • Example:

This forces the failover of the MDS daemon with rank 0.

ceph fs mds stop

Stops a specific MDS daemon.

  • Example:

This stops the MDS daemon with rank 0.

3. Snapshot Management

ceph fs snap create

Creates a snapshot of a CephFS directory.

  • Example:

This creates a snapshot mysnap of the root directory / in the filesystem myfs.

ceph fs snap ls

Lists all snapshots for a specified CephFS directory.

  • Example:

This lists all snapshots in the root directory / of the myfs filesystem.

ceph fs snap rm

Removes a specific snapshot from a CephFS directory.

  • Example:

This removes the snapshot mysnap from the root directory / in the myfs filesystem.

4. Quota Management

ceph fs set-quota

Sets a quota on a specified directory in a CephFS filesystem.

  • Example:

This sets a 100MB quota on the directory /mydir in the filesystem myfs.

ceph fs get-quota

Retrieves the current quota settings for a specified directory in a CephFS filesystem.

  • Example:

This retrieves the quota settings for the directory /mydir in the filesystem myfs.

5. Client Management

ceph fs authorize

Authorizes a Ceph client to access a specific CephFS filesystem with read, write, or full permissions.

  • Example:

This authorizes the client client.myclient to have read/write access to the myfs filesystem.

ceph fs deauthorize

Revokes a Ceph client’s access to a specified filesystem.

  • Example:

This revokes the client client.myclient's access to the myfs filesystem.

6. Mounting a CephFS Filesystem

Mount via Kernel Client

You can mount a CephFS using the Linux kernel client.

  • Example:

This mounts the CephFS root / to the /mnt/mycephfs directory, using the admin keyring for authentication.

Mount via FUSE

You can also mount CephFS using the FUSE client.

  • Example:

This mounts the CephFS filesystem myfs to /mnt/mycephfs using the FUSE client.

7. Pool Management

ceph fs add_data_pool

Adds a new data pool to an existing CephFS filesystem.

  • Example:

This adds a new data pool cephfs_data2 to the filesystem myfs.

ceph fs set default_pool

Sets a pool as the default data or metadata pool for a CephFS filesystem.

  • Example:

This sets cephfs_data2 as the default data pool for the filesystem myfs.

Conclusion

CephFS offers rich functionality for managing distributed filesystems within a Ceph cluster. From creating filesystems and managing MDS daemons to handling quotas, snapshots, and client permissions, the ceph fs suite of commands provides the necessary tools to administer CephFS instances effectively. Additionally, CephFS integrates with Ceph’s powerful object store, making it a flexible solution for large-scale, high-performance storage environments

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