ZFS - Pool Fails to Import on Array Start

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Special, cache, and log VDEVs are comprised of partitions on a group of 3 NVME drives.

 

This is not supported, at least not for now, each device can only be used once for a pool, and zfs must be on partition #1.

In the release notes, it mentions reporting zpools topologies that won't import, so I wanted to file the report so it can be added to the list of ZFS topology possibilities to be considered going forward.  The idea of splitting up a very high performance NVME into partitions and using those partitions to serve multiple functions is quite common when balancing availability and performance in ZFS special, cache, and log VDEVs.

Edited May 19, 2023 by Keliaxx

It would be a good option, but because Unraid uses one device per slot, and that device will have a single function for the pool, it might not be easy to implement, but lets see what LT thinks.

As a bit of an addendum around NVME and ZFS, but also applicable to NVME in general is that underprovisioning NVME is extremely common for extending its service life.  A lot of modern controllers no longer provide the option to underprovision or create separate domains at the hardware level, so it is now accomplished through partitioning.  Fully supporting NVME use cases really does require having the ability to work with partitions as well as entire devices IMHO.

LT, any thoughts to offer up on this?

@limetech What is the gameplan here with regards to zfs volumes that use high performance nvme partitions for cache/special/zil?