Chapter 6. Optimizing ephemeral storage

Pods use ephemeral storage for their internal operation such as saving temporary files. The lifetime of this ephemeral storage does not extend beyond the life of the individual pod, and this ephemeral storage cannot be shared across pods.

Prior to OpenShift Container Platform 3.10, ephemeral local storage was exposed to pods through the container’s writable layer, logs directory, and EmptyDir volumes. Issues related to the lack of local storage accounting and isolation include the following:

Ephemeral storage is still exposed to pods in the same way, but there are new methods for implementing requests and limits on pods' consumption of ephemeral storage.

It is important to understand that ephemeral storage is shared among all pods in the system, and that OpenShift Container Platform does not provide any mechanism for guaranteeing any level of service beyond the requests and limits established by the administrator and users. For example, ephemeral storage does not provide any guarantees of throughput, I/O operations per second, or any other measure of storage performance.

A node’s local storage can be broken into primary and secondary partitions. Primary partitions are the only ones you can use for ephemeral local storage. There are two supported primary partitions, root and runtime.