Re: [PATCH v6 00/16] nvmet: add target passthru commands support

Sagi Grimberg
2019-07-29T16:15:11Z

>> This is different from multipath on say a multi-controller PCI device
>> and trying to expose both those controllers through passthru. this is
>> where the problems we are discussing come up.
>
> I *think* there is some confusion. I *think* Sagi is talking about network multi-path (i.e. the ability for the host to connect to a controller on the target via two different network paths that fail-over as needed). I *think* Logan is talking about multi-port PCIe NVMe devices that allow namespaces to be accessed via more than one controller over PCIe (dual-port NVMe SSDs being the most obvious example of this today).

Yes, I was referring to fabrics multipathing which is somewhat
orthogonal to the backend pci multipathing (unless I'm missing
something).

>> But it's the multipath through different ports that
>> seems important for fabrics. ie. If I have a host with a path through
>> RDMA and a path through TCP they should both work and allow fail over.
>
> Yes, or even two paths that are both RDMA or both TCP but which take a different path through the network from host to target.
>
>> Our real-world use case is to support our PCI device which has a bunch
>> of vendor unique commands and isn't likely to support multiple
>> controllers in the foreseeable future.
>
> I think solving passthru for single-port PCIe controllers would be a good start.

Me too.