It's always struck me as odd that everyone uses dedicated drives for Metadata Special Devices on their ZFS pools considering the metadata size is much smaller than common drive sizes and you are taking up four PCIe lanes per disk just to store the metadata.

I get it in the enterprise or production, but homelab? Seems overkill.

With most consumer motherboards offering a limited number of slots, I got to thinking; what if you mirrored two NVMe drives for redundancy and either partitioned it or created a VHD and told Unraid to use that as the Metadata Special Device? Some searching seems to show that that is possible, but I wanted to ask around to get second opinions.

So say you had a mirrored pool of NVMe with 1TB of usable storage and HDD pool was 30TB. Well, if you did what I'm thinking, you can split the NVMe pool in half and dedicate half to metadata and the other half can still be usable for VMs, Docker, etc.

I imagine in homelab, this would be safe to do because the wear on these drives even from doing all that extra work would be low.

I do have a test system I can set up to try it with, but I thought that before I went through all the trouble with that I would ask here.

Anyone have any thoughts?

Unraid currently only supports one partition per device, so you cannot use the same device for multiple vdevs.

2 hours ago, JorgeB said:

Unraid currently only supports one partition per device, so you cannot use the same device for multiple vdevs.

And using a VHD (.img) file for metadata?

Also not supported, at least not officially, and I never tested it, but I suspect it won't work; it must be an assigned device.

2 hours ago, JorgeB said:

Also not supported, at least not officially, and I never tested it, but I suspect it won't work; it must be an assigned device.

Hmm, I know some people virtualize Unraid. Do you think it would accept a VHD created by the hypervisor?

I don't know for sure, but as long as it's an assignable device, it should, but doesn't mean it's recommended.