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Lesson 8. Theoretical Doubt: Relation between PV and PVC

Hello everyone.
How are you all doing?

I am doing the labs for lesson 8: VOLUMES AND DATA and I have a question. I don't understand how the persistentVolumes are related to the PersistentVolumeClaim.
I mean, if I create a PV:

  1. apiVersion: v1
  2. kind: PersistentVolume
  3. metadata:
  4. name: pvvol-1
  5. spec:
  6. capacity:
  7. storage: 1Gi
  8. accessModes:
  9. - ReadWriteMany
  10. persistentVolumeReclaimPolicy: Retain
  11. nfs:
  12. path: /opt/sfw
  13. server: k8scp
  14. readOnly: false

I can see that it is not claimed by anyone.

  1. ~$ kubectl get pv
  2. NAME CAPACITY ACCESS MODES RECLAIM POLICY STATUS CLAIM STORAGECLASS REASON AGE
  3. pvvol-1 1Gi RWX Delete Available 87s

Now if I create a PVC:

  1. apiVersion: v1
  2. kind: PersistentVolumeClaim
  3. metadata:
  4. name: pvc-one
  5. spec:
  6. accessModes:
  7. - ReadWriteMany
  8. resources:
  9. requests:
  10. storage: 200Mi

Now I can see that the PV is claimed by the PVC pvc-one.

  1. ~$ kubectl get pv
  2. NAME CAPACITY ACCESS MODES RECLAIM POLICY STATUS CLAIM STORAGECLASS REASON AGE
  3. pvvol-1 1Gi RWX Delete Bound small/pvc-one 2m47s

But I have not specified that the PV pvvol-1 is claimed by pvc-one. So how are they related?

Thank you very much and best regards.

Comments

  • Posts: 57

    @dgsison A control loop in the master watches for new PVCs, finds a matching PV (if possible). In our case it checks only size to be matched. You also can use key volumeName key in your PVC manifest to assign it explicitly. For example:

    1. apiVersion: v1
    2. kind: PersistentVolumeClaim
    3. metadata:
    4. name: pvc-one
    5. spec:
    6. accessModes:
    7. - ReadWriteMany
    8. resources:
    9. requests:
    10. storage: 2000Mi
    11. volumeName: pvvol-1

    You can find more here: https://kubernetes.io/docs/concepts/storage/persistent-volumes/

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