I don't work on 2TB+ memory servers, but one of my servers is close to 1TB of RAM.
PostgreSQL scales nicely here. Main thing you're getting is a huge disk cache. Makes repeated queries nice and fast. Still I/O bound to some extent though.
Redis will scale nicely as well. But it won't be I/O bound.
Honestly, if you really need 1TB+ it's usually going to be for numerically intensive code. This kind of code is generally written to be highly vectorizable so the hardware prefetcher will usually mask memory access latency and you get massive speedups by having your entire dataset in memory. Algorithms that can memoize heavily also benefit greatly.
PostgreSQL scales nicely here. Main thing you're getting is a huge disk cache. Makes repeated queries nice and fast. Still I/O bound to some extent though.
Redis will scale nicely as well. But it won't be I/O bound.
Honestly, if you really need 1TB+ it's usually going to be for numerically intensive code. This kind of code is generally written to be highly vectorizable so the hardware prefetcher will usually mask memory access latency and you get massive speedups by having your entire dataset in memory. Algorithms that can memoize heavily also benefit greatly.