DirectIO For OpenZFS Shows Very Promising Performance

Written by Michael Larabel in Linux Storage on 10 November 2021 at 06:05 AM EST. 12 Comments
Running the past two days was the annual OpenZFS Developer Summit. One of the most interesting presentations from this virtual event was on the status of DirectIO (O_DIRECT) support for the OpenZFS file-system and the performance boost it can offer in relevant areas.

Brian Atkinson of the Los Alamos National Laboratory presented at the developer summit around the DirectIO support for OpenZFS. The work ultimately boils down to the DirectIO merge request open for OpenZFS since February 2020. This support aims to allow bypassing ZFS' ARC when issuing reads/writes with a particular focus on improving the performance for Zpools on NVMe solid-state drives as well as other cases where ARC just gets in the way.

When using speedy NVMe drives as VDEVs, he found a 1.5~3x speed-up using the DirectIO mode.

The Linux support/performance at least appears to be in good shape while the FreeBSD performance testing is ongoing. The pull request remains open but could land potentially for OpenZFS 3.0.

Those interested in Brian's presentation on DirectIO for OpenZFS can see the slide deck.
Related News
About The Author
Michael Larabel

Michael Larabel is the principal author of and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 20,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and automated benchmarking software. He can be followed via Twitter, LinkedIn, or contacted via

Popular News This Week