وحدات التخزين الدائمة ومطالباتها

In Kubernetes, Pods are designed to be temporary and replaceable. If a Pod crashes or is rescheduled, any data stored directly within it is lost.

This ephemeral nature is great for stateless applications, but what about applications that need to store data persistently, like databases or file servers?

A Persistent Volume (PV) is a piece of storage in the cluster that has been provisioned by an administrator or dynamically by Kubernetes.

It's an abstraction of the underlying storage (like a cloud disk, NFS share, or local disk), making it available for use by Pods without them needing to know the storage's specifics.

Each PV has specific characteristics:

• Capacity: The size of the storage, e.g., 10Gi.
• Access Modes: How the storage can be mounted by Pods.
• Reclaim Policy: What happens to the volume after a Pod is done using it.

These properties help Kubernetes match storage requests to available volumes.

PV Access Modes define how the volume can be mounted:

• ReadWriteOnce (RWO): The volume can be mounted as read-write by a single node.
• ReadOnlyMany (ROX): The volume can be mounted as read-only by many nodes.
• ReadWriteMany (RWX): The volume can be mounted as read-write by many nodes.

Not all storage types support all modes. For example, a local disk typically only supports RWO.

A PV's Reclaim Policy dictates what happens to the underlying storage when the PV is released from its claim:

• Retain: Manual reclamation. Data remains, administrator must manually delete.
• Delete: The underlying storage is automatically deleted along with the PV. This is common for dynamically provisioned volumes.
• Recycle: (Deprecated) Wipes the volume and makes it available again.

Retain is useful for critical data that needs manual review before deletion.

A Persistent Volume Claim (PVC) is a request for storage by a user or application.

Think of it like a request for a specific type and size of storage. Instead of directly interacting with PVs, Pods request storage through PVCs.

PVCs provide a layer of abstraction, allowing developers to request storage without knowing the underlying infrastructure details.

When a PVC is created, Kubernetes tries to find a suitable PV to bind it to. This process is called binding.

It looks for PVs that meet the PVC's requirements:

• Capacity (size)
• Access Modes
• Storage Class (if specified)

Once bound, the PV is exclusively reserved for that PVC.

Here's how you might define a simple hostPath Persistent Volume. This type uses a directory on the node's filesystem, primarily for single-node testing.

Try running this example (kubectl apply -f pv.yaml):

Now, let's create a Persistent Volume Claim that requests 1Gi of storage with ReadWriteOnce access. It will bind to our my-pv if available.

Try running this example (kubectl apply -f pvc.yaml):

Finally, let's see how a Pod can use the storage provided by our PVC. We reference the PVC in the Pod's volumes section and then mount it into a container.

Try running this example (kubectl apply -f pod.yaml):

Understanding the distinct roles of Persistent Volumes (PVs) and Persistent Volume Claims (PVCs) is crucial for managing storage in Kubernetes.

Which statement accurately describes the primary role of a Persistent Volume (PV)?

Great job! You've learned how Kubernetes manages persistent storage:

• Persistent Volumes (PVs) abstract physical storage resources.
• Persistent Volume Claims (PVCs) are user requests for storage.
• PVs have capacity, access modes (RWO, ROX, RWX), and reclaim policies (Retain, Delete).
• PVCs bind to available PVs, and Pods then use PVCs to mount storage.

This system allows applications to reliably store data, even when Pods are recreated or moved.