Sure, I have no knowledge of cache, so if btrfs is the recommended, then lets go with that. Can you see from the diagnostics (or some statistics) if the drives spin up often (or too often) ? I dont write that often to the server/array. If I write to cache first, can it be set up to automatically move - or do I manually have to move from cache to array ?
Do I need to physically remove the cache drive to format it ? Or can we do it while its connected inside the server ?