File storage

The Ceph File System, or CephFS, is a POSIX-compliant file system built on top of Ceph’s distributed object store, RADOS.

The ceph-fs charm deploys the metadata server daemon (MDS), which is the underlying management software for CephFS. The charm is deployed within the context of an existing Charmed Ceph cluster.

Highly available CephFS is achieved by deploying multiple MDS servers (i.e. multiple ceph-fs application units).

CephFS deployment

To deploy a three-node MDS cluster in a pre-existing Ceph cluster:

juju deploy -n 3 --to lxd:0,lxd:1,lxd:2 ceph-fs
juju add-relation ceph-fs:ceph-mds ceph-mon:mds

Here the three ceph-fs units are containerised, where new containers are placed on existing machines 0, 1, and 2.

CephFS is now fully set up.

CephFS client usage

This section will provide optional instructions for verifying the CephFS service by setting up a simple client environment. Deploy the client using the steps provided in the Client setup appendix.

Note: These instructions are based upon the native capabilities of the Linux kernel (v.4.x).
A kernel driver will allow the client to mount CephFS as a regular file system.

An example deployment will have a juju status output similar to the following:

Model  Controller     Cloud/Region     Version  SLA          Timestamp
ceph   my-controller  my-maas/default  2.8.1    unsupported  19:34:16Z

App          Version  Status  Scale  Charm     Store       Rev  OS      Notes
ceph-fs      15.2.3   active      3  ceph-fs   jujucharms   24  ubuntu  
ceph-mon     15.2.3   active      3  ceph-mon  jujucharms   49  ubuntu  
ceph-osd     15.2.3   active      3  ceph-osd  jujucharms  304  ubuntu  
ceph-client  20.04    active      1  ubuntu    jujucharms   15  ubuntu  

Unit            Workload  Agent  Machine  Public address  Ports  Message
ceph-client/0*  active    idle   3             ready
ceph-fs/0       active    idle   0/lxd/0             Unit is ready
ceph-fs/1       active    idle   1/lxd/0             Unit is ready
ceph-fs/2*      active    idle   2/lxd/0             Unit is ready
ceph-mon/0      active    idle   0/lxd/1             Unit is ready and clustered
ceph-mon/1      active    idle   1/lxd/1             Unit is ready and clustered
ceph-mon/2*     active    idle   2/lxd/1             Unit is ready and clustered
ceph-osd/0      active    idle   0             Unit is ready (2 OSD)
ceph-osd/1*     active    idle   1             Unit is ready (2 OSD)
ceph-osd/2      active    idle   2             Unit is ready (2 OSD)

The client host is represented by the ceph-client/0 unit.

Verify that the filesystem name set up by the ceph-fs charm is ‘ceph-fs’:

juju ssh ceph-mon/0 "sudo ceph fs ls"


name: ceph-fs, metadata pool: ceph-fs_metadata, data pools: [ceph-fs_data ]

Create a CephFS user (‘test’) with read/write permissions at the root of the ‘ceph-fs’ filesystem, collect the user’s keyring file, and transfer it to the client:

juju ssh ceph-mon/0 "sudo ceph fs authorize ceph-fs client.test / rw" \
  | tee ceph.client.test.keyring

juju scp ceph.client.test.keyring ceph-client/0:

Connect to the client:

juju ssh ceph-client/0

From the CephFS client,

Configure the client using the keyring file and set up the correct permissions:

sudo mv ~ubuntu/ceph.client.test.keyring /etc/ceph
sudo chmod 600 /etc/ceph/ceph.client.test.keyring
sudo chown root: /etc/ceph/ceph.client.test.keyring

Note: The key installed on a client host authorises access to the CephFS filesystem for the host itself, and not to a particular user.

Mount the CephFS filesystem and create a test file:

sudo mkdir /mnt/cephfs
sudo mount -t ceph :/ /mnt/cephfs -o name=test
sudo mkdir /mnt/cephfs/work
sudo chown ubuntu: /mnt/cephfs/work
touch /mnt/cephfs/work/test

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