FS volumes and subvolumes

FS volumes and subvolumes

A single source of truth for CephFS exports is implemented in the volumesmodule of the Ceph Manager daemon (ceph-mgr). The OpenStack sharedfile system service (manila), Ceph Container Storage Interface (CSI),storage administrators among others can use the common CLI provided by theceph-mgr volumes module to manage the CephFS exports.

The ceph-mgr volumes module implements the following file system exportabstactions:

FS volumes, an abstraction for CephFS file systems
FS subvolumes, an abstraction for independent CephFS directory trees
FS subvolume groups, an abstraction for a directory level higher than FSsubvolumes to effect policies (e.g., File layouts) across aset of subvolumes

Some possible use-cases for the export abstractions:

FS subvolumes used as manila shares or CSI volumes
FS subvolume groups used as manila share groups

Requirements

Nautilus (14.2.x) or a later version of Ceph
Cephx client user (see User Management) withthe following minimum capabilities:

mon 'allow r'
mgr 'allow rw'

FS Volumes

Create a volume using:

$ ceph fs volume create <vol_name>

This creates a CephFS file system and its data and metadata pools. It also triesto create MDSes for the filesystem using the enabled ceph-mgr orchestratormodule (see Orchestrator CLI) , e.g., rook.

Remove a volume using:

$ ceph fs volume rm <vol_name> [--yes-i-really-mean-it]

This removes a file system and its data and metadata pools. It also tries toremove MDSes using the enabled ceph-mgr orchestrator module.

List volumes using:

$ ceph fs volume ls

FS Subvolume groups

Create a subvolume group using:

$ ceph fs subvolumegroup create <vol_name> <group_name> [--pool_layout <data_pool_name> --uid <uid> --gid <gid> --mode <octal_mode>]

The command succeeds even if the subvolume group already exists.

When creating a subvolume group you can specify its data pool layout (seeFile layouts), uid, gid, and file mode in octal numerals. By default, thesubvolume group is created with an octal file mode ‘755’, uid ‘0’, gid ‘0’ and data poollayout of its parent directory.

Remove a subvolume group using:

$ ceph fs subvolumegroup rm <vol_name> <group_name> [--force]

The removal of a subvolume group fails if it is not empty or non-existent.‘–force’ flag allows the non-existent subvolume group remove command to succeed.

Fetch the absolute path of a subvolume group using:

$ ceph fs subvolumegroup getpath <vol_name> <group_name>

List subvolume groups using:

$ ceph fs subvolumegroup ls <vol_name>

Create a snapshot (see Experimental Features) of asubvolume group using:

$ ceph fs subvolumegroup snapshot create <vol_name> <group_name> <snap_name>

This implicitly snapshots all the subvolumes under the subvolume group.

Remove a snapshot of a subvolume group using:

$ ceph fs subvolumegroup snapshot rm <vol_name> <group_name> <snap_name> [--force]

Using the ‘–force’ flag allows the command to succeed that would otherwisefail if the snapshot did not exist.

List snapshots of a subvolume group using:

$ ceph fs subvolumegroup snapshot ls <vol_name> <group_name>

FS Subvolumes

Create a subvolume using:

$ ceph fs subvolume create <vol_name> <subvol_name> [--size <size_in_bytes> --group_name <subvol_group_name> --pool_layout <data_pool_name> --uid <uid> --gid <gid> --mode <octal_mode>]

The command succeeds even if the subvolume already exists.

When creating a subvolume you can specify its subvolume group, data pool layout,uid, gid, file mode in octal numerals, and size in bytes. The size of the subvolume isspecified by setting a quota on it (see Quotas). By default asubvolume is created within the default subvolume group, and with an octal filemode ‘755’, uid of its subvolume group, gid of its subvolume group, data pool layout ofits parent directory and no size limit.

Remove a subvolume using:

$ ceph fs subvolume rm <vol_name> <subvol_name> [--group_name <subvol_group_name> --force]

The command removes the subvolume and its contents. It does this in two steps.First, it move the subvolume to a trash folder, and then asynchronously purgesits contents.

The removal of a subvolume fails if it has snapshots, or is non-existent.‘–force’ flag allows the non-existent subvolume remove command to succeed.

Resize a subvolume using:

$ ceph fs subvolume resize <vol_name> <subvol_name> <new_size> [--group_name <subvol_group_name>] [--no_shrink]

The command resizes the subvolume quota using the size specified by ‘new_size’.‘–no_shrink’ flag prevents the subvolume to shrink below the current used size of the subvolume.

The subvolume can be resized to an infinite size by passing ‘inf’ or ‘infinite’ as the new_size.

Fetch the absolute path of a subvolume using:

$ ceph fs subvolume getpath <vol_name> <subvol_name> [--group_name <subvol_group_name>]

List subvolumes using:

$ ceph fs subvolume ls <vol_name> [--group_name <subvol_group_name>]

Create a snapshot of a subvolume using:

$ ceph fs subvolume snapshot create <vol_name> <subvol_name> <snap_name> [--group_name <subvol_group_name>]

Remove a snapshot of a subvolume using:

$ ceph fs subvolume snapshot rm <vol_name> <subvol_name> <snap_name> [--group_name <subvol_group_name> --force]