Wondering, what happens if you create a mirror cache with an NVME and physical hard drive in it (both 2TB)?  Is btrfs smart enough to realize that one drive is much faster and send the majority of the reads that way, or does it just balance between X number of drives, sending 1/X the IO to each drive?

 

I'd like to see the activity on the physical drive be basically only writes and have all the reads come off the NVME because it's so much faster.

6 hours ago, Overtaxed said:

Is btrfs smart enough to realize that one drive is much faster and send the majority of the reads that way

Writes to a mirror will always have to go to both drives, and it can never be faster than the slowest drive, for reads it could use the faster device, btrfs currently doesn't do that, though it's planned for the future.