You got your units mixed up buddy. True for the 118GB drive, 6 drive writes per day is 708GB per day. But 5 years is 1825 days so 1825x708GB=1,292,100GB≈1300TB≈1.3PB. That is 1.3 Peta bytes not Terra bytes. For reference the 1TB 980 Pro (which is TLC despite the name Pro) has endurance of 600TB and the 2TB 980Pro has 1200TB.Hmm, I am not sure if its really worth it. Although 6DPWD seems incredible, the drive is just 118GB. 6 drive writes = 708GB a day. 5yrs = 1.3TB
What you are suggesting is not really caching. You are essentially suggesting using the HDD (or the slower SSD) + the fast SSD al for storage. For caching there is not much point using a larger drive than 64GB and that was and the reason Intel's RST for years was topping out at 64GB as the optimum capacity for caching. Probably they managed to extent that to 128GB but in any case if you have a larger a capacity drive to use as cache you will essentially be using that drive for storage not for caching for the bigger drive you want to cache for. Also if cost is not an issue you can just buy more (in number) fast SSDs. You have to think big though. If we talk about a data centre with tens of 1000s of drives 400 dollars per drive difference becomes several millions of dollars difference.A 960GB drive can cache way more data than 118GB one. The drive cost ~USD485. Even if the 118GB Xpoint cost USD85, I don't think 400 makes a big difference to a server.
Depends on what you are caching and why. If you occasionally run simulations or other workloads that have a huge memory footprint and isn't particularly performance-critical because you just need to be able to complete it, I could imagine spending $90 on a caching SSD for your system that can handle everything else you need to do with 32GB of DDR4 being a far more attractive option than getting 128+GB of DDR4 and a quad-channel platform that supports it if necessary.For caching there is not much point using a larger drive than 64GB