> I wouldn't be surprised if they could get around the trickiest constraint, which is how many hard drives you can plug in to a non-mainframe machine for historical image storage.
Some commodity machines use external SAS to connect to more disk boxes. IMHO, there's not a real reason to keep images and tweets on the same server if you're going to need an external disk box anyway. Rather than getting a 4u server with a lot of disks and a 4u additional disk box, you may as well get 4u servers with a lot of disks each, use one for tweets and the other for images. Anyway, images are fairly easy to scale horizontally, there's not much simplicity gained by having them all in one host, like there is for tweets.
Yah like I say in the post, the exactly one machine thing is just for fun and as an illustration of how far vertical scaling can go, practically I'd definitely scale storage with many sharded smaller storage servers.
Some commodity machines use external SAS to connect to more disk boxes. IMHO, there's not a real reason to keep images and tweets on the same server if you're going to need an external disk box anyway. Rather than getting a 4u server with a lot of disks and a 4u additional disk box, you may as well get 4u servers with a lot of disks each, use one for tweets and the other for images. Anyway, images are fairly easy to scale horizontally, there's not much simplicity gained by having them all in one host, like there is for tweets.