Red Hat Summit4.4. Lifecycle of a volume and claim
PVs are resources in the cluster. PVCs are requests for those resources and also act as claim checks to the resource. The interaction between PVs and PVCs have the following lifecycle.
4.4.1. Provision storage
In response to requests from a developer defined in a PVC, a cluster administrator configures one or more dynamic provisioners that provision storage and a matching PV.
4.4.2. Bind claims
When you create a PVC, you request a specific amount of storage, specify the required access mode, and create a storage class to describe and classify the storage. The control loop in the master watches for new PVCs and binds the new PVC to an appropriate PV. If an appropriate PV does not exist, a provisioner for the storage class creates one.
The size of all PVs might exceed your PVC size. This is especially true with manually provisioned PVs. To minimize the excess, Red Hat build of MicroShift binds to the smallest PV that matches all other criteria.
Claims remain unbound indefinitely if a matching volume does not exist or can not be created with any available provisioner servicing a storage class. Claims are bound as matching volumes become available. For example, a cluster with many manually provisioned 50Gi volumes would not match a PVC requesting 100Gi. The PVC can be bound when a 100Gi PV is added to the cluster.
4.4.3. Use pods and claimed PVs
Pods use claims as volumes. The cluster inspects the claim to find the bound volume and mounts that volume for a pod. For those volumes that support multiple access modes, you must specify which mode applies when you use the claim as a volume in a pod.
Once you have a claim and that claim is bound, the bound PV belongs to you for as long as you need it. You can schedule pods and access claimed PVs by including persistentVolumeClaim in the pod’s volumes block.
If you attach persistent volumes that have high file counts to pods, those pods can fail or can take a long time to start. For more information, see When using Persistent Volumes with high file counts in OpenShift, why do pods fail to start or take an excessive amount of time to achieve "Ready" state?.
4.4.4. Release a persistent volume
When you are finished with a volume, you can delete the PVC object from the API, which allows reclamation of the resource. The volume is considered released when the claim is deleted, but it is not yet available for another claim. The previous claimant’s data remains on the volume and must be handled according to policy.
4.4.5. Reclaim policy for persistent volumes
The reclaim policy of a persistent volume tells the cluster what to do with the volume after it is released. A volume’s reclaim policy can be Retain, Recycle, or Delete.
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Retainreclaim policy allows manual reclamation of the resource for those volume plugins that support it. -
Recyclereclaim policy recycles the volume back into the pool of unbound persistent volumes once it is released from its claim.
The Recycle reclaim policy is deprecated in Red Hat build of MicroShift 4. Dynamic provisioning is recommended for equivalent and better functionality.
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Deletereclaim policy deletes both thePersistentVolumeobject from Red Hat build of MicroShift and the associated storage asset in external infrastructure, such as Amazon Elastic Block Store (Amazon EBS) or VMware vSphere.
Dynamically provisioned volumes are always deleted.
4.4.6. Reclaiming a persistent volume manually
When a persistent volume claim (PVC) is deleted, the underlying logical volume is handled according to the reclaimPolicy.
Procedure
To manually reclaim the PV as a cluster administrator:
Delete the PV by running the following command:
$ oc delete pv <pv_name>The associated storage asset in the external infrastructure, such as an AWS EBS, GCE PD, Azure Disk, or Cinder volume, still exists after the PV is deleted.
- Clean up the data on the associated storage asset.
- Delete the associated storage asset. Alternately, to reuse the same storage asset, create a new PV with the storage asset definition.
The reclaimed PV is now available for use by another PVC.
4.4.7. Changing the reclaim policy of a persistent volume
You can change the reclaim policy of a persistent volume.
Procedure
List the persistent volumes in your cluster:
$ oc get pvExample output
NAME CAPACITY ACCESSMODES RECLAIMPOLICY STATUS CLAIM STORAGECLASS REASON AGE pvc-b6efd8da-b7b5-11e6-9d58-0ed433a7dd94 4Gi RWO Delete Bound default/claim1 manual 10s pvc-b95650f8-b7b5-11e6-9d58-0ed433a7dd94 4Gi RWO Delete Bound default/claim2 manual 6s pvc-bb3ca71d-b7b5-11e6-9d58-0ed433a7dd94 4Gi RWO Delete Bound default/claim3 manual 3sChoose one of your persistent volumes and change its reclaim policy:
$ oc patch pv <your-pv-name> -p '{"spec":{"persistentVolumeReclaimPolicy":"Retain"}}'Verify that your chosen persistent volume has the right policy:
$ oc get pvExample output
NAME CAPACITY ACCESSMODES RECLAIMPOLICY STATUS CLAIM STORAGECLASS REASON AGE pvc-b6efd8da-b7b5-11e6-9d58-0ed433a7dd94 4Gi RWO Delete Bound default/claim1 manual 10s pvc-b95650f8-b7b5-11e6-9d58-0ed433a7dd94 4Gi RWO Delete Bound default/claim2 manual 6s pvc-bb3ca71d-b7b5-11e6-9d58-0ed433a7dd94 4Gi RWO Retain Bound default/claim3 manual 3sIn the preceding output, the volume bound to claim
default/claim3now has aRetainreclaim policy. The volume will not be automatically deleted when a user deletes claimdefault/claim3.
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