Enable Ceph Shared File System (CephFS)¶

TechPreview

The Ceph Shared File System, or CephFS, provides the capability to create read/write shared file system Persistent Volumes (PVs). These PVs support the ReadWriteMany access mode for the FileSystem volume mode. CephFS deploys its own daemons called MetaData Servers or Ceph MDS. For details, see Ceph Documentation: Ceph File System.

Note

By design, CephFS data pool and metadata pool must be replicated only.

Note

Due to the Technology Preview status of the feature, the following restrictions apply:

CephFS is supported as a Kubernetes CSI plugin that only supports creating Kubernetes Persistent Volumes based on the FileSystem volume mode. For a complete modes support matrix, see Ceph CSI: Support Matrix.
Ceph Controller supports only one CephFS installation per Ceph cluster.
Ceph Controller supports only one data pool per CephFS installation.

CephFS specification¶

The KaaSCephCluster CR includes the spec.cephClusterSpec.sharedFilesystem.cephFS section with the following CephFS parameters:

CephFS specification¶
Parameter	Description
`name`	CephFS instance name.
`dataPool`	CephFS data pool spec that should only contain `replicated` and `failureDomain` parameters. The `failureDomain` parameter may be set to `osd` or `host`, defining the failure domain across which the data will be spread. Can use only `replicated` settings. For example: cephClusterSpec: sharedFilesystem: cephFs: - name: cephfs-store dataPool: replicated: size: 3 failureDomain: host where `replicated.size` is the number of full copies of data on multiple nodes. Warning Modifying of `dataPool` on a deployed CephFS has no effect. You can manually adjust pool settings through the Ceph CLI. However, for any changes in `dataPool`, Mirantis recommends re-creating CephFS.
`metadataPool`	CephFS metadata pool spec that should only contain `replicated` and `failureDomain` parameters. The `failureDomain` parameter may be set to `osd` or `host`, defining the failure domain across which the data will be spread. Can use only `replicated` settings. For example: cephClusterSpec: sharedFilesystem: cephFs: - name: cephfs-store metadataPool: replicated: size: 3 failureDomain: host where `replicated.size` is the number of full copies of data on multiple nodes. Warning Modifying `metadataPool` on a deployed CephFS has no effect. You can manually adjust pool settings through the Ceph CLI. However, for any changes in `metadataPool`, Mirantis recommends re-creating CephFS.
`preserveFilesystemOnDelete`	Defines whether to delete the data and metadata pools if CephFS is deleted. Set to `true` to avoid occasional data loss in case of human error. However, for security reasons, Mirantis recommends setting `preserveFilesystemOnDelete` to `false`.
`metadataServer`	Metadata Server settings correspond to the Ceph MDS daemon settings. Contains the following fields: `activeCount` - the number of active Ceph MDS instances. As load increases, CephFS will automatically partition the file system across the Ceph MDS instances. Rook will create double the number of Ceph MDS instances as requested by `activeCount`. The extra instances will be in the standby mode for failover. Mirantis recommends specifying this parameter to `1` and increasing the MDS daemons count only in case of high load. `activeStandby` - defines whether the extra Ceph MDS instances will be in active standby mode and will keep a warm cache of the file system metadata for faster failover. The instances will be assigned by CephFS in failover pairs. If `false`, the extra Ceph MDS instances will all be in passive standby mode and will not maintain a warm cache of the metadata. The default value is `false`. `resources` - represents Kubernetes resource requirements for Ceph MDS pods. For example: cephClusterSpec: sharedFilesystem: cephFs: - name: cephfs-store metadataServer: activeCount: 1 activeStandby: false resources: # example, non-prod values requests: memory: 1Gi cpu: 1 limits: memory: 2Gi cpu: 2

Enable CephFS¶

Open the corresponding Cluster resource for editing:
```
kubectl -n <managedClusterProjectName> edit cluster
```
Substitute <managedClusterProjectName> with the corresponding value.

In the spec.providerSpec.helmReleases section, enable the CephFS CSI plugin installation:

spec:
  providerSpec:
    helmReleases:
    ...
    - name: ceph-controller
      ...
      values:
        ...
        rookExtraConfig:
          csiCephFsEnabled: true

You can also override the CSI Ceph FS gRPC and liveness metrics port. For example, if an application is already using the default CephFS ports 9092 and 9082, which may cause conflicts on the node.

spec:
  providerSpec:
    helmReleases:
    ...
    - name: ceph-controller
      ...
      values:
        ...
        rookExtraConfig:
          csiCephFsEnabled: true
          csiCephFsGPCMetricsPort: "9092" # should be a string
          csiCephFsLivenessMetricsPort: "9082" # should be a string

Rook will enable the CephFS CSI plugin and provisioner.

Save Cluster and close the editor.
Open the KaasCephCluster CR of a managed cluster for editing:
```
kubectl edit kaascephcluster -n <managedClusterProjectName>
```
Substitute <managedClusterProjectName> with the corresponding value.

In the sharedFilesystem section, specify parameters according to CephFS specification. For example:

spec:
  cephClusterSpec:
    sharedFilesystem:
      cephFs:
      - name: cephfs-store
        dataPool:
          replicated:
            size: 3
          failureDomain: host
        metadataPool:
          replicated:
            size: 3
          failureDomain: host
        metadataServer:
          activeCount: 1
          activeStandby: false

Define the mds role for the corresponding nodes where Ceph MDS daemons should be deployed. Mirantis recommends labeling only one node with the mds role. For example:
```
spec:
  cephClusterSpec:
    nodes:
      ...
      worker-1:
        roles:
        ...
        - mds
```
Save KaaSCephCluster and close the editor.

Once CephFS is specified in the KaaSCephCluster CR, Ceph Controller will validate it and request Rook to create CephFS. Then Ceph Controller will create a Kubernetes StorageClass, required to start provisioning the storage, which will operate the CephFS CSI driver to create Kubernetes PVs.

Note

The Storage Class will be named as <cephfs-name>-cephfs. Also, the provisioner will be set to rook-ceph.cephfs.csi.ceph.com. To use CephFS for provisioning volumes, StorageClass must match <cephfs-name>-cephfs in PersistentVolumeClaim (PVC). For example:

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: cephfs-pvc-example
  namespace: some-namespace
spec:
  storageClassName: <cephfs-name>-cephfs
  ...