What is a Persistent Volume For Database?

This article briefly introduces the topic, covering persistent storage and its reclaim policy. Listed below are some benefits of persistent volumes. For more information, read on.

Persistent Volume

A persistent volume defines a storage volume in the system. It may be mounted on a specific path and can provide an abstraction of the underlying storage system. Persistent volumes may also specify a storage class name to identify the volume as an independent resource. In many cases, a persistent volume is not a standalone resource but a storage asset. A persistent volume is a file or directory that persists over time, typical for database containers. While most containers are stateless, a database container may need a data directory that survives a container restart. The persistent volume provides a virtual device that can be mounted into a container without resetting the container’s hard disk. Its use in cloud-native deployments is fundamental.

Persistent Volume Claim

A persistent volume (PVC) is a storage object that stores data. It has the same features like a volume but is unique. However, there are a few essential differences between a PVC and a volume. For example, PVCs can be consumed, while PVs can only be used in one node at a time. T Pods request access to a persistent disk and get it via PVC. The data on this persistent disk remains even after the persistent volume claim has been deleted. If you have a stateless application, it’s better to use Stateful Set with Read Write Once volumes. Pods will need to know that the second will continue to work when the first Pod is destroyed. The second Pod will not be deleted since the first hasn’t started.

Persistent storage

If you’re running a complex software project requiring data to be re-used by multiple instances, persistent storage is the way. It’s beneficial when a single instance won’t need data for years. Persistent storage is a storage format that retains data even after the power to the system is turned off. Data can be stored on nonvolatile media such as flash memory, hard disks, or tape. The data can be retrieved again and is therefore highly flexible. For this reason, persistent storage can be used for more than just databases. Some databases can even run on disks. Regardless of how you use the data, it’s worth considering persistent storage. One of the most common types of persistent storage is system images. These images must have sufficient RAM to store the state of the system. For example, changes are made after the last picture is lost if a system crashes. However, saving images for each change can be incredibly time-consuming, especially on slower systems. Another type of persistence is journaling. Journaling is another type of persistent storage and stores events in a log before applying them to the system. At startup, the system reads the journal and reapplies the changes to the data.

Persistent Volume reclaim policy

A persistent volume (PV) storage asset is available to pods running in a cluster. PVCs are created through a storage class. When a PVC is created, the reclaim policy for the PV is set in the Storage Class object. The default value is deleted. The other option, allowing Volume Expansion, allows the storage class to grow the PV’s volume. This is useful for users who need to expand their volume capacity but do not want to remove it permanently. A PV can be consumed or released if the owner has permission to consume it. The corresponding PVC object must be edited to expand or contract a PV. The resulting expansion will occur on the volume’s current size. However, the administrator cannot change the PVC’s name after creating it. The default Storage Class is the first storage class that a PVC will be bound to.
By Mussarat Zafar

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