Special device / Fusion Pool - hardware recommendations?


May 6, 2023

I've tried looking for info on "special device" or "fusion pool" but despite several conversations I can't seem to find any real info on hardware choices and recommendations.

All the threads seem to be just "don't use, the whole pool will be gone when you lose the metadata vdev!!!" in its simplicity.
This is true, but is special vdev really somehow worse than HDD pool? Or why is it so feared?

Of course, adding a vdev to the pool increases the risk of failure considerably, but as I understand it, in exactly the same way as expanding the pool with more data vdevs, or have I misunderstood something?
The assumption that the special vdev uses a mirror of the same level as the data vdev itself has fault tolerance. (for example RaidZ2 + 3-way mirror)

What kind of SSD / NVME disks do you use? What kind of experiences do you have?

I would be most interested in used enterprise devices.
However, I have very little understanding of enterprise-level SSD disks, so their wide spectrum of model numbers doesn't really mean anything to me.
Any recommendations?

Have you noticed a big effect while using special vdev in home use, where most of the data is large media files and photos?

Patrick M. Hausen

Hall of Famer
Nov 25, 2013
I run Fusion pools with redundant prosumer SSDs from Samsung. They work great. I monitor SMART values and recorded SSD wear with Scrutiny and Grafana. I recommend using metadata vdevs if the primary use is multi user SMB with lots of concurrent access and small files.