When you want to feed your GPUs with what they need (model, weights, data), that kind of hoops slow you down exponentially. You need to be able to stream data to pinned memory, or to the GPU directly (hence GPUDirect) to keep your cards saturated.

This is why systems like Weka exist, and why Lustre is still being developed and polished. These systems reach tremendous speeds. This is not an exaggeration when you connect terabits of bandwidth to these storage systems.