With this setting and all files being>2M, (approximately) every other tail would end up on sVDEV. I wonder what the end goal of this setting was… Looks unreasonable to me.
As a rule of thumb, metadata is about 0.3% of the data size. For 128K records… So it is 300GB of metadata for 100TB of data (with 128K records). Or it’s 18.75G with 2M records. Your metadata is 14G for 65T of data. Looks like the rule kinda works. I, for one, have 6GB of metadata for 16TB of data. My pool has different files (not only media), but for the media I used 4M records.
The takeaway – 128GB sVDEV would probably be enough in the general case (with only metadata performance boost in mind) for sub-100TB pools. As well as all these “2x256G SSD for my apps and VMs”. Although no VMs can be saved on sVDEV as of now…