Persistent Volumes

Persistent Volumes (PVs) in Kubernetes provide a mechanism for managing storage resources independently of individual Pods. Unlike ephemeral storage, which is tied to the lifecycle of a Pod, PVs ensure data persists across Pod restarts and rescheduling, enabling stateful applications to function reliably in a Kubernetes cluster.

In Kubernetes, storage resources are abstracted through the Persistent Volume framework, which decouples storage provisioning from application deployment. A Persistent Volume (PV) represents a piece of storage that has been provisioned in the cluster, while a Persistent Volume Claim (PVC) is a request for storage made by an application.

Key characteristics of Persistent Volumes include:

• Decoupled Storage Management: PVs exist independently of Pods, allowing storage to persist even when Pods are deleted or rescheduled.
• Dynamic and Static Provisioning: Storage can be provisioned manually by administrators (static provisioning) or automatically by storage classes (dynamic provisioning).
• Access Modes: PVs support multiple access modes, such as ReadWriteOnce (RWO), ReadOnlyMany (ROX), and ReadWriteMany (RWX), defining how storage can be accessed by Pods.
• Reclaim Policies: When a PV is no longer needed, it can be retained, recycled, or deleted based on its configured reclaim policy.
• Storage Classes: Kubernetes allows administrators to define different types of storage using StorageClasses, enabling automated provisioning of PVs based on workload requirements.

In simplyblock, each PV is connected to the storage cluster with NVMe-oF (TCP, RoCEv2) through multiple paths to multiple storage nodes, with the primary path being a local loopback when possible. Each PV is implemented as a namespace in an NVMe-oF subsystem on the storage nodes.