Does TrueNAS support using a virtual disk in a storage pool?

I recently purchased a new NAS / Server and while I'm waiting for it to arrive I'm planning out my storage and RAID configurations.

I'ce mostly decided on using 5 20TB or 24TB drives in RAID z2 as my primary storage pool. I'll just use a 500GB nvme as a read cache. But I still have a gen 4 by 4 nvme slot available, and I'm considering buying a stupidly large nvme drive to put in it.

Problem is, I want some fault tolerance, so I'm wondering if I can just make a virtual drive in my primary pool and use a RAID mirror between the nvme and the virtual drive to make my secondary pool.

Would this work? Or would the performance overhead and instibility make this a fool's errand?