4.2. Persistent storage overview

PVCs are specific to a namespace, and are created and used by developers as a means to use a PV. PV resources on their own are not scoped to any single namespace; they can be shared across the entire Red Hat build of MicroShift cluster and claimed from any namespace. After a PV is bound to a PVC, that PV can not then be bound to additional PVCs. This has the effect of scoping a bound PV to a single namespace.

PVs are defined by a PersistentVolume API object, which represents a piece of existing storage in the cluster that was either statically provisioned by the cluster administrator or dynamically provisioned using a StorageClass object. It is a resource in the cluster just like a node is a cluster resource.

PVs are volume plugins like Volumes but have a lifecycle that is independent of any individual pod that uses the PV. PV objects capture the details of the implementation of the storage, be that LVM, the host filesystem such as hostpath, or raw block devices.

Like PersistentVolumes, PersistentVolumeClaims (PVCs) are API objects, which represents a request for storage by a developer. It is similar to a pod in that pods consume node resources and PVCs consume PV resources. For example, pods can request specific levels of resources, such as CPU and memory, while PVCs can request specific storage capacity and access modes. Access modes supported by OpenShift Container Platform are also definable in Red Hat build of MicroShift. However, because Red Hat build of MicroShift does not support multi-node deployments, only ReadWriteOnce (RWO) is pertinent.