On Wed, May 30, 2018 at 06:02:06PM -0400, Mike Snitzer wrote: > Because once nvme_core.multipath=N is set: native NVMe multipath is then > not accessible from the same host. The goal of this patchset is to give > users choice. But not limit them to _only_ using dm-multipath if they > just have some legacy needs.
Choise by itself really isn't an argument. We need a really good use case for all the complexity, and so far none has been presented. > Tough to be convincing with hypotheticals but I could imagine a very > obvious usecase for native NVMe multipathing be PCI-based embedded NVMe > "fabrics" (especially if/when the numa-based path selector lands). But > the same host with PCI NVMe could be connected to a FC network that has > historically always been managed via dm-multipath.. but say that > FC-based infrastructure gets updated to use NVMe (to leverage a wider > NVMe investment, whatever?) -- but maybe admins would still prefer to > use dm-multipath for the NVMe over FC. That is a lot of maybes. If they prefer the good old way on FC then can easily stay with SCSI, or for that matter use the global switch off. > > This might sound stupid to you, but can't users that desperately must > > keep using dm-multipath (for its mature toolset or what-not) just > > stack it on multipath nvme device? (I might be completely off on > > this so feel free to correct my ignorance). > > We could certainly pursue adding multipath-tools support for native NVMe > multipathing. Not opposed to it (even if just reporting topology and > state). But given the extensive lengths NVMe multipath goes to hide > devices we'd need some way to piercing through the opaque nvme device > that native NVMe multipath exposes. But that really is a tangent > relative to this patchset. Since that kind of visibility would also > benefit the nvme cli... otherwise how are users to even be able to trust > but verify native NVMe multipathing did what it expected it to? Just look at the nvme-cli output or sysfs. It's all been there since the code was merged to mainline.
