Yeah those are pretty spendy. I know one comes with extra guaranteed bandwidth which is kind of handy if you’re sharing a small number of cache nodes among a lot of servers. But we were doing okay running r6 for cache, though my coworker who knew the ritual for migrating them did eventually get a little boost out of switching us to r7’s. The latency wasn’t great and I don’t think faster network cards would have helped that. There was already plenty of incentive for us to do per-request promise caching to avoid pulling the same keys multiple times in a request but that was necessary because the business model forced the architecture to tolerate nondeterminism. The cost per request was what eventually killed them (the economy dipped and customers ran to cheaper vendors), but I’ve never seen a company survive being stupid for as long as this place did.
