What is Persistent Storage?

Persistent storage is a term that often comes up in any discussion about container technology such as Kubernetes. Here is a deeper look.

Persistent storage is a term that often comes up in any discussion about container technology such as Kubernetes. Here is an attempt to define the term and show how it is related to container technology.

What is Persistent Storage?

Persistent storage, also referred to as non-volatile storage, can be defined as any data storage device that is capable of retaining data after the power supply to the said device is shut off. Common types of persistent storage are magnetic media like hard disk drives, tape, and optical storage devices such as DVDs. This form of storage system can be in the form of a file, object, or block storages.

Mostly, persistent storage is a fundamental part of any storage system, regardless of whether it is a single drive, shared or networked, or even cloud storage. Because of this commonality, persistence is rarely mentioned while discussing the specs for storage systems or devices.

How Does It Relate to Containerization?

Contrary to the statement above, there is one exception that came about with the recent growth of virtualized computing environments, bringing persistence into the conversation. Containerization has recently become a popular choice to bundle applications using operating systems to create mobile yet discreet modules that can be formed and destroyed as per requirements. During the early days of container technology, they didn't support persistent storage. As a result, the data created with a containerized app would disappear when the app finished its work and the container was destroyed.

However, several storage and software developers storage have recently adopted ways to retain any data created by the applications within the containers and maintain the said data in familiar storage volumes. These volumes are usually paired with stateful applications (like, available databases) even if the application is shut down or even if the processing is done. These advances in container storage solve the retaining issue concerning the temporary storage volumes that live and die within the applications running from the containers.

Persistence with SSDs

Solid State Drives or SSDs are also types of persistent storage. Still, there is some difference compared to the other types - SSDs do not have any moving parts, internally or with the media access drives.

Furthermore, some types of solid state storage, for example, RAM chips and cache systems, are typically volatile or non-persistent storage devices. The data within them is erased when continuous power ceases to flow into the machines. On the other hand, some types of non-volatile and flash-based RAM are persistent; relying on battery power when the primary source power is cut off. Super-capacitors are also used in achieving persistence. RAM persistence is seen as important as it can prevent data loss in the event of reboots or crashes.

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