Safe power draw

[epixoip]

It's not weird behavior and it's not specific to Nvidia by any means. You need host buffers for the device buffers. When you allocate a buffer on the device, you have to allocate a buffer on the host as well. Otherwise how else would you get the results? If you have 8GB of VRAM per device, you could conceivably allocate 100% of that (yes, a misinterpretation of the OpenCL spec results in most vendors limiting each allocation to 25% of VRAM, but you can in fact allocate multiple buffers.) If you're allocating 8GB of buffers on each device, and you have eight devices, you could conceivably need to allocate 64GB of buffers on the host as well. If the host cannot allocate 64GB of RAM for Hashcat, it will crash with CL_OUT_OF_HOST_MEMORY. At an absolute minimum available host memory should never be less than VRAM * 0.25, but the rule of thumb is RAM >= VRAM.

Keep in mind that password cracking is not cryptocurrency mining, and most mining rig setups suck for password cracking.