Q100700: Changing Nuke/Hiero/Nuke Studio's EXR reading mode to potentially improve EXR read performance

Pete

Updated: May 12, 2026 22:00

Created: January 20, 2026 15:57

SUMMARY

This article will outline how you may be able to improve EXR read performance, especially over a network.

MORE INFORMATION

In Nuke 12.2v7, and later, we have introduced optional modes for reading EXRs, which has helped a number of users to improve their read performance in Nuke, Hiero and Nuke Studio.

To use this functionality, you will need to set the FN_EXR_FILE_READ_MODE environment variable on your system, which can be specified to use normal, mmap, buffer, or default mode.

We would recommend first setting the environment variable to buffer mode, like so:

FN_EXR_FILE_READ_MODE=buffer

For more information about setting environment variables, please refer to the following article:
Q100015: How to set environment variables

If this environment variable has been set correctly, you should see the following output in the Terminal, the first time you import an EXR into your Nuke/Hiero/Nuke Studio session:

FN_EXR_FILE_READ_MODE: using specified mode, buffer

You can then repeat this process for the other modes (normal and mmap) to see which yields the best results for your network setup.

FURTHER READING

If you are still experiencing poor EXR read performance in Nuke/Hiero/Nuke Studio, please open a Support request to let us know the exact issue encountered and the troubleshooting steps that have been taken.

For more information on how to open a Support request, please refer to this article:
Q100064: How to raise a support ticket