Enabling Replication in CSI Unity
Container Storage Modules (CSM) Replication sidecar is a helper container that is installed alongside a CSI driver to facilitate replication functionality. Such CSI drivers must implement
CSI driver for Dell Unity supports necessary extension calls from
dell-csi-extensions. To be able to provision replicated volumes you would need to do the steps described in these sections.
On Storage Array
Be sure to configure replication between multiple Unity instances using instructions provided by Unity storage.
Ensure you installed CRDs and replication controller in your clusters.
To verify you have everything in order you can execute these commands:
- Check controller pods
Pods should be
kubectl get pods -n dell-replication-controller
- Check that controller config map is properly populated
kubectl get cm -n dell-replication-controller dell-replication-controller-config -o yaml
datafield should be properly populated with cluster-id of your choosing and, if using multi-cluster installation, your
targets:parameter should be populated by a list of target clusters IDs.
If you don’t have something installed or something is out-of-place, please refer to installation instructions in installation-repctl or installation.
Installing Driver With Replication Module
To install the driver with replication enabled, you need to ensure you have set
controller.replication.enabled in your copy of example
Here is an example of what that would look like:
... # controller: configure controller specific parameters controller: ... # replication: allows to configure replication replication: enabled: true image: dellemc/dell-csi-replicator:v1.2.0 replicationContextPrefix: "unity" replicationPrefix: "replication.storage.dell.com" ...
You can leave other parameters like
replicationPrefix as they are.
After enabling the replication module, you can continue to install the CSI driver for Unity following the usual installation procedure. Just ensure you’ve added the necessary array connection information to secret.
NOTE: you need to install your driver on ALL clusters where you want to use replication. Both arrays must be accessible from each cluster.
Creating Storage Classes
To provision replicated volumes, you need to create adequately configured storage classes on both the source and target clusters.
A pair of storage classes on the source, and target clusters would be essentially
mirrored copies of one another.
You can create them manually or with the help of
Manual Storage Class Creation
You can find a sample replication enabled storage class in the driver repository here.
It will look like this:
apiVersion: storage.k8s.io/v1 kind: StorageClass metadata: name: unity-replication provisioner: csi-unity.dellemc.com reclaimPolicy: Delete volumeBindingMode: Immediate parameters: replication.storage.dell.com/isReplicationEnabled: "true" replication.storage.dell.com/remoteStorageClassName: "unity-replication" replication.storage.dell.com/remoteClusterID: "target" replication.storage.dell.com/remoteSystem: "APM000000002" replication.storage.dell.com/rpo: "5" replication.storage.dell.com/ignoreNamespaces: "false" replication.storage.dell.com/volumeGroupPrefix: "csi" replication.storage.dell.com/remoteStoragePool: pool_002 replication.storage.dell.com/remoteNasServer: nas_124 arrayId: "APM000000001" protocol: "NFS" storagePool: pool_001 nasServer: nas_123
Let’s go through each parameter and what it means:
replication.storage.dell.com/isReplicationEnabledif set to
true, will mark this storage class as replication enabled, just leave it as
replication.storage.dell.com/remoteStorageClassNamepoints to the name of the remote storage class. If you are using replication with the multi-cluster configuration you can make it the same as the current storage class name.
replication.storage.dell.com/remoteClusterIDrepresents the ID of a remote cluster. It is the same id you put in the replication controller config map.
replication.storage.dell.com/remoteSystemis the name of the remote system that should match whatever
clusterNameyou called it in
replication.storage.dell.com/rpois an acceptable amount of data, which is measured in units of time, that may be lost due to a failure.
replication.storage.dell.com/ignoreNamespaces, if set to
trueUnity driver, it will ignore in what namespace volumes are created and put every volume created using this storage class into a single volume group.
replication.storage.dell.com/volumeGroupPrefixrepresents what string would be appended to the volume group name to differentiate them.
NOTE: To configure the VolumeGroupPrefix, the name format of '<volumeGroupPrefix>-<namespace>-<Cluster Name>-<rpo>’ cannot be more than 63 characters.
arrayIdis a unique identifier of the storage array you specified in array connection secret.
nasServerid of the Nas server of local array to which the allocated volume will belong.
storagePoolis the storage pool of the local array.
After figuring out how storage classes would look, you just need to go and apply them to your Kubernetes clusters with
Storage Class creation with
repctl can simplify storage class creation by creating a pair of mirrored storage classes in both clusters
(using a single storage class configuration) in one command.
To create storage classes with
repctl you need to fill up the config with necessary information.
You can find an example here, copy it, and modify it to your needs.
If you open this example you can see a lot of similar fields and parameters you can modify in the storage class.
Let’s use the same example from manual installation and see what config would look like:
targetClusterID: "cluster-2" sourceClusterID: "cluster-1" name: "unity-replication" driver: "unity" reclaimPolicy: "Retain" replicationPrefix: "replication.storage.dell.com" remoteRetentionPolicy: RG: "Retain" PV: "Retain" parameters: arrayId: source: "APM000000001" target: "APM000000002" storagePool: source: pool_123 target: pool_124 rpo: "0" ignoreNamespaces: "false" volumeGroupPrefix: "prefix" protocol: "NFS" nasServer: source: nas_123 target: nas_123
After preparing the config, you can apply it to both clusters with
repctl. Before you do this, ensure you’ve added your clusters to
repctl via the
To create storage classes just run
./repctl create sc --from-config <config-file> and storage classes would be applied to both clusters.
After creating storage classes you can make sure they are in place by using
./repctl get storageclasses command.
Provisioning Replicated Volumes
After installing the driver and creating storage classes, you are good to create volumes using newly created storage classes.
On your source cluster, create a PersistentVolumeClaim using one of the replication-enabled Storage Classes. The CSI Unity driver will create a volume on the array, add it to a VolumeGroup and configure replication using the parameters provided in the replication enabled Storage Class.
Supported Replication Actions
The CSI Unity driver supports the following list of replication actions: