Q:Cache size 200TB volume

Using DS1821+, 64GB RAM, 10GBe card, 2x DX-517.

I want to add 2x NVME Read/Write cache for this unit with \~200TB volume SHR-2 BTRFS. Mixed usage.

AI gave me sometimes 2x 1TB, sometimes 2x 2TB or even 2X 4TB with pinned metadata.

Any one with experience adding NVME cache to very large volumes?