To dive slightly into that: You don't necessarily want to sacrifice space for a read cache disk: having more space can reduce writes as you do less replacement.
But where you want endurance is for a ZIL SLOG (the write cache, effectively). Optane was great for this because of really high endurance and very low latency persistent writes, but, ... Farewell, dear optane, we barely knew you.
The 400GB optane card had an endurance of 73 PB written. Pretty impressive, though at almost $3/GB it was really expensive.
This would likely work but as a sibling commenter noted, you're probably better off with a purpose-built, high endurance drive. Since it's a write cache, just replace it a little early.
AIUI the slog is only for synchronous writes; most people using zfs at home don’t do any of those (unless you set sync=always which is not the default).
Terrific for a hobby project, build farm, or even a business in a prototype stage (buy 3-4 then).
Hardly acceptable in a larger setting where continuity in 10 years is important. Of course, not the exact same part available in 10 years (which is not unheard of, though), but something compatible or at least comparable.
If you have a scenario where Optane makes sense today, in 10 years it'll be cost effective to use at least that much DRAM, backed by whatever storage is mainstream then and whatever capacitors or batteries you need to safely flush that DRAM to storage.
A dead-end product on clearance sale isn't the right choice for projects where you need to keep a specific mission-critical machine running for a decade straight. But for a lot of projects, all that really matters is that in a few years you can set up a new system with equal or better performance characteristics and not need to re-write your application to work well on the new hardware. I think all of the (vanishingly few) scenarios where Optane NVMe SSDs make sense fall into the latter category. (I feel sorry for anyone who invested significant effort into writing software to use Optane DIMMs.)
To dive slightly into that: You don't necessarily want to sacrifice space for a read cache disk: having more space can reduce writes as you do less replacement.
But where you want endurance is for a ZIL SLOG (the write cache, effectively). Optane was great for this because of really high endurance and very low latency persistent writes, but, ... Farewell, dear optane, we barely knew you.
The 400GB optane card had an endurance of 73 PB written. Pretty impressive, though at almost $3/GB it was really expensive.
This would likely work but as a sibling commenter noted, you're probably better off with a purpose-built, high endurance drive. Since it's a write cache, just replace it a little early.
AIUI the slog is only for synchronous writes; most people using zfs at home don’t do any of those (unless you set sync=always which is not the default).
https://jrs-s.net/2019/05/02/zfs-sync-async-zil-slog/
Under provisioning is the standard recommendation for ZFS SSD cache/log/l2arc drives since those special types were a thing.
Optane 905p goes for $500 a piece (1T) I believe.
For how long?
Terrific for a hobby project, build farm, or even a business in a prototype stage (buy 3-4 then).
Hardly acceptable in a larger setting where continuity in 10 years is important. Of course, not the exact same part available in 10 years (which is not unheard of, though), but something compatible or at least comparable.
If you have a scenario where Optane makes sense today, in 10 years it'll be cost effective to use at least that much DRAM, backed by whatever storage is mainstream then and whatever capacitors or batteries you need to safely flush that DRAM to storage.
A dead-end product on clearance sale isn't the right choice for projects where you need to keep a specific mission-critical machine running for a decade straight. But for a lot of projects, all that really matters is that in a few years you can set up a new system with equal or better performance characteristics and not need to re-write your application to work well on the new hardware. I think all of the (vanishingly few) scenarios where Optane NVMe SSDs make sense fall into the latter category. (I feel sorry for anyone who invested significant effort into writing software to use Optane DIMMs.)
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In a larger setting you're looking at a much shorter hardware refresh time than 10 years.