Filesystem Storage Overview
A filesystem storage (also named shared filesystem) can be mounted with read/write permission from multiple pods. This may be useful for applications which can be clustered using a shared filesystem.
This example runs a shared filesystem for the kube-registry.
This guide assumes you have created a Rook cluster as explained in the main quickstart guide
Multiple Filesystems Support¶
Multiple filesystems are supported as of the Ceph Pacific release.
Create the Filesystem¶
Create the filesystem by specifying the desired settings for the metadata pool, data pools, and metadata server in the
CephFilesystem CRD. In this example we create the metadata pool with replication of three and a single data pool with replication of three. For more options, see the documentation on creating shared filesystems.
Save this shared filesystem definition as
The Rook operator will create all the pools and other resources necessary to start the service. This may take a minute to complete.
To confirm the filesystem is configured, wait for the mds pods to start:
To see detailed status of the filesystem, start and connect to the Rook toolbox. A new line will be shown with
ceph status for the
mds service. In this example, there is one active instance of MDS which is up, with one MDS instance in
standby-replay mode in case of failover.
Before Rook can start provisioning storage, a StorageClass needs to be created based on the filesystem. This is needed for Kubernetes to interoperate with the CSI driver to create persistent volumes.
Save this storage class definition as
If you've deployed the Rook operator in a namespace other than "rook-ceph" as is common change the prefix in the provisioner to match the namespace you used. For example, if the Rook operator is running in "rook-op" the provisioner value should be "rook-op.rbd.csi.ceph.com".
Create the storage class.
The CephFS CSI driver uses quotas to enforce the PVC size requested.
Only newer kernels support CephFS quotas (kernel version of at least 4.17). If you require quotas to be enforced and the kernel driver does not support it, you can disable the kernel driver and use the FUSE client. This can be done by setting
CSI_FORCE_CEPHFS_KERNEL_CLIENT: false in the operator deployment (
operator.yaml). However, it is important to know that when the FUSE client is enabled, there is an issue that during upgrade the application pods will be disconnected from the mount and will need to be restarted. See the upgrade guide for more details.
Consume the Shared Filesystem: K8s Registry Sample¶
As an example, we will start the kube-registry pod with the shared filesystem as the backing store. Save the following spec as
Create the Kube registry deployment:
You now have a docker registry which is HA with persistent storage.
Kernel Version Requirement¶
If the Rook cluster has more than one filesystem and the application pod is scheduled to a node with kernel version older than 4.7, inconsistent results may arise since kernels older than 4.7 do not support specifying filesystem namespaces.
Consume the Shared Filesystem: Toolbox¶
Once you have pushed an image to the registry (see the instructions to expose and use the kube-registry), verify that kube-registry is using the filesystem that was configured above by mounting the shared filesystem in the toolbox pod. See the Direct Filesystem topic for more details.
To clean up all the artifacts created by the filesystem demo:
To delete the filesystem components and backing data, delete the Filesystem CRD.
Data will be deleted if preserveFilesystemOnDelete=false**.
Note: If the "preserveFilesystemOnDelete" filesystem attribute is set to true, the above command won't delete the filesystem. Recreating the same CRD will reuse the existing filesystem.
Advanced Example: Erasure Coded Filesystem¶
The Ceph filesystem example can be found here: Ceph Shared Filesystem - Samples - Erasure Coded.