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Windows Storage

This page provides an storage overview specific to the Windows operating system.

Persistent storage

Windows has a layered filesystem driver to mount container layers and create a copy filesystem based on NTFS. All file paths in the container are resolved only within the context of that container.

  • With Docker, volume mounts can only target a directory in the container, and not an individual file. This limitation does not apply to containerd.
  • Volume mounts cannot project files or directories back to the host filesystem.
  • Read-only filesystems are not supported because write access is always required for the Windows registry and SAM database. However, read-only volumes are supported.
  • Volume user-masks and permissions are not available. Because the SAM is not shared between the host & container, there's no mapping between them. All permissions are resolved within the context of the container.

As a result, the following storage functionality is not supported on Windows nodes:

  • Volume subpath mounts: only the entire volume can be mounted in a Windows container
  • Subpath volume mounting for Secrets
  • Host mount projection
  • Read-only root filesystem (mapped volumes still support readOnly)
  • Block device mapping
  • Memory as the storage medium (for example, emptyDir.medium set to Memory)
  • File system features like uid/gid; per-user Linux filesystem permissions
  • Setting secret permissions with DefaultMode (due to UID/GID dependency)
  • NFS based storage/volume support
  • Expanding the mounted volume (resizefs)

Kubernetes volumes enable complex applications, with data persistence and Pod volume sharing requirements, to be deployed on Kubernetes. Management of persistent volumes associated with a specific storage back-end or protocol includes actions such as provisioning/de-provisioning/resizing of volumes, attaching/detaching a volume to/from a Kubernetes node and mounting/dismounting a volume to/from individual containers in a pod that needs to persist data.

Volume management components are shipped as Kubernetes volume plugin. The following broad classes of Kubernetes volume plugins are supported on Windows:

In-tree volume plugins

The following in-tree plugins support persistent storage on Windows nodes:

Last modified November 01, 2022 at 3:38 PM PST: Fix links about flexvolume (35665871da)