@matrix Wow, mastodon is that big? Interesting. I wonder why.
I'd still say you're better off with a writeback cache on XFS.
Here's a video that explains it:
https://youtu.be/WEvCxFLHOM0Basically, you just make a partition on NVME drive, and set it to be a writeback cache. You'll read and write to the NVME and it'll be lazily synced back to the slab.
A disadvantage is a drive failure of the cache drive will almost always result in data loss. NVME is RAID 10 tho so no real worries there.