ARC and/or L2ARC
I been thinking on suggesting/requesting this "idea" and just recently found out it is an actual thing that is already released. I'm wondering if Unraid will be adding this feature as it would be a great addition. For those that don't know, you can find more details about what ARC is below.
(credits to zfsbuilds.com)
TL;DR - Have SSD drives that also cache most accessed data and/or maybe to cache data depending on the administrators settings that best fit the server
I don't think that is going to be implemented.
Cache drive kind of acts as an L2ARC for writing. Nothing for read. Closest you get there is if a file is still on the cache drive. I believe any unused memory is also used for writing to the array.
It has been requested that mover add a "move older than xxx date". This would allow us to keep the cache drive somewhat full with the most recent files, kind of acting as an L2ARC for reading.