According to this calculator:
Video bitrate calculator | web.forret.com (http://web.forret.com/tools/video_fps.asp?width=7680&height=4320&fps=24&space=yuv444&depth=16)

8k workflow using YUV4:4:4 and 16bit color depth will take 4.78GB PER SECOND
4k workflow using the same will take 1.19GB PER SECOND

how do commercial studios handle this worfklow? tons of SSDs? what were they doing pre-SSD days?

My guess is something like HP Storageworks with a 40 or 80+ Gb backbone in combination with a decent workstation, like the HP Proliant DL 580. Mind you, I'm only guessing.

See http://www8.hp.com/ca/en/products/disk-storage/product-detail.html?oid=5157544#!tab=models and the workstation below.

Keep in mind, the storage solution is way more expensive than a simple $ 200 K workstation.

There are companies that specialise in providing storage for postproduction. Editshare is one, they seem to now have 4k 40 Gigabit Ethernet Shared Storage Options - EditShare (http://www.editshare.com/about/about-us/press/item/158-pr-40-gigabit-ethernet)

I assume it's similar to these: Post Production - EditShare (http://www.editshare.com/markets/post-production)

Storage Options - EditShare (http://www.editshare.com/products/storage-options)