The TrueNAS installer doesn't have a way to use anything less than the full device. This is usually a waste of resources when installing to a modern NVMe which is usually several hundred of GB. TrueNAS SCALE will use only a few GB for its system files so installing to a 16GB partition would be helpful.
The easiest way to solve this is to modify the installer script before starting the installation process.
Basic guide to deploying a simple 4-node Lustre cluster on Centos 7 using VMs from Virtualbox.
Updated and adapted fork of dleske/Three-Node-LustreFS-Cluster-Quickstart.md, which was based on joshuar/Three-Node-LustreFS-Cluster-Quickstart.md, which was based on Intel's How to Create and Mount a Lustre Filesystem. I've taken a lot of inspiration from Oak Ridge National Laboratory slides about Lustre and the official documentation, especially the network configuring section.
The document in its current form has not much to do with those ones but I definitely got them as a starting point.
Note: I am a newbie to Lustre so this overview is extremely light and specif