TrueNAS SCALE Bluefin is adding the capability to natively support the Docker Overlay filesystem and its drivers. This significantly improves the handling and scalability of systems running many Container instances.

Docker (and Kubernetes) uses an Overlay file system to manage the layers of pre-built container distribution images. Overlay file systems allow for creating a union mapping of two or more directories: a list of lower directories and an upper directory. The lower directories of the filesystem are read only, whereas the upper directory can be used for both reads and writes.

Until now, OpenZFS has not natively supported these Overlay filesystem primitives, and the result has been some major inefficiencies in how Linux Containers have scaled up. Last year, it became a high priority for TrueNAS to solve this limitation for future releases of SCALE. Recently, the new OverlayFS capability has passed its initial battery of testing and has landed in the RC1 release of SCALE 22.12 (Bluefin).

With this OverlayFS addition, OpenZFS becomes a superior file system for managing container storage. Not only is OverlayFS supported, but all the significant advantages of OpenZFS over other Linux file systems are inherited. The benefits inherited by TrueNAS SCALE include:

• Copy-on-Write snapshots and clones
• Integrated volume management with multiple RAID levels
• In-line compression, encryption, and deduplication
• Efficient, encrypted replication
• Effective Read and Write Caching
• On-line expansion and self-healing

TrueNAS SCALE Bluefin (22.12-RC.1) includes these major improvements to OpenZFS and is scheduled for November 15th. TrueNAS SCALE’s Application Infrastructure will automatically switch to using the OverlayFS container drivers and users should see an immediate improvement to CPU utilization and a minimization of on-disk dataset & snapshot utilization. Developers and testers can test using the latest nightly. TrueNAS SCALE users can expect to see a Bluefin RELEASE version at the end of 2022.

TrueNAS SCALE users will see much simpler operation of Docker Containers and Apps (Helm Charts). Both the built-in Apps and other community-run App Catalogs will benefit. System admins will see both improved performance and much less clutter when administering snapshots.

The OpenZFS software for this improvement has been contributed back to the OpenZFS community with the expectation it may become a standard capability of future OpenZFS releases as well as TrueNAS SCALE. The GitHub link for the OpenZFS-OverlayFS feature is here.

For more discussion on containers, check out our Community Forums and Discord Channel where you can post and collaborate. We also welcome any questions on TrueNAS appliances on our contact form or live chat on our websites.