Open Shift PV and PVC - unix1998/technical_notes GitHub Wiki

In OpenShift (and Kubernetes as a whole), Persistent Volumes (PVs) and Persistent Volume Claims (PVCs) work together to manage storage for your applications. While they both deal with storage, they serve distinct purposes:

Persistent Volume (PV):

  • Represents a physical or virtual storage resource.
  • This storage can come from various sources like:
    • Host local storage (physical disks on the cluster nodes)
    • Cloud storage providers (e.g., AWS EBS, Azure Disks)
    • Network storage (e.g., NFS, iSCSI)
  • A PV defines the characteristics of the storage, including:
    • Capacity (size)
    • Access Modes (ReadWriteOnce, ReadWriteMany)
    • Storage class (optional) - specifies performance characteristics or backing store type
  • PVs are managed by the cluster administrator. They can be statically provisioned (manually configured) or dynamically provisioned using storage classes.

Persistent Volume Claim (PVC):

  • Represents a request for storage from an application or pod.
  • A PVC specifies the storage requirements of an application, including:
    • Storage request (desired capacity)
    • Access Modes (Read/Write needs)
    • Storage class (optional) - preference for a specific type of storage

Why Both? - Separation of Concerns:

  • PVs and PVCs provide a decoupled approach to storage management, offering several benefits:

    • Flexibility for Applications: Applications don't need to be aware of the underlying physical storage details. They simply request the storage they need through PVCs.
    • Simplified Management: Cluster administrators can manage the PVs (storage resources) independently of how applications use them (through PVCs). This separation allows for easier scaling and provisioning of storage.
    • Resource Control: PVCs define application storage requests, allowing for resource control and preventing applications from exceeding their allocated storage quotas.

Analogy:

Think of PVs as different types of apartments (studios, one-bedrooms, etc.) in a building (cluster). PVCs are like tenant requests, specifying the size and features they need (e.g., one-bedroom with a balcony). The building manager (cluster administrator) assigns apartments (PVs) that meet the tenant requests (PVCs) based on availability.

In summary:

  • PVs represent the storage resources available.
  • PVCs represent the storage requests from applications.
  • This decoupled approach provides flexibility, simplifies management, and promotes resource control for storage within your OpenShift environment.

################################################ In OpenShift, Persistent Volumes (PVs) and Persistent Volume Claims (PVCs) have distinct roles and different levels of access and management requirements.

  1. Persistent Volumes (PVs):

    • Administration: PVs are managed by cluster administrators. This is because PVs are cluster-wide resources that need to be configured with specific storage backend details, such as NFS, iSCSI, or cloud storage options.
    • Role: Only users with the Cluster Admin role or equivalent permissions can create, manage, and delete PVs. This is to ensure that storage resources are properly configured and allocated without compromising the integrity and availability of the storage infrastructure.

  2. Persistent Volume Claims (PVCs):

    • Usage: PVCs are used by individual users to request storage resources. When a PVC is created, it binds to an appropriate PV based on the storage class, capacity, and access modes defined.
    • Role: Regular users, including developers, can create, manage, and delete PVCs within their own namespaces. This allows users to request and utilize storage resources without needing cluster-wide permissions.
    • Function: PVCs abstract the underlying storage details from the users, allowing them to focus on their applications and workloads.

Summary

  • PVs can only be managed by users with the Cluster Admin role.
  • PVCs can be created and managed by regular users within their respective namespaces.

This separation of roles ensures that storage resources are managed securely and efficiently, with cluster administrators handling the provisioning and configuration of storage infrastructure while users can easily request and use the storage they need for their applications.