Thx, for me it was not possible to post this
And some mor informations what is possible with something like this monster
Interesting, it looks like no such kind of hard limit is set in modern Linux system. Instead, there is a kernel configuration option named "Maximum number of GPUs" under Linux, and we can set it to an arbitrarily large value freely.
In practice, I can confirm that more than 16 GPUs running on a single motherboard is possible, for I have just built such a rig by myself (with 18 GPUs, on a Supermicro X9DRX board). See https://devtalk.nvidia.com/default/topic/649542/cuda-setup-and-installation/18-gpus-in-a-single-rig-...
However, just like the FASTRA2, my rig is also built with NV cards. Hope AMD can solve the driver issue so we can build a similar or even more powerful rig with AMD cards.