On Wed, May 30 2018 at 5:20pm -0400, Sagi Grimberg <s...@grimberg.me> wrote: > Moreover, I also wanted to point out that fabrics array vendors are > building products that rely on standard nvme multipathing (and probably > multipathing over dispersed namespaces as well), and keeping a knob that > will keep nvme users with dm-multipath will probably not help them > educate their customers as well... So there is another angle to this.
Noticed I didn't respond directly to this aspect. As I explained in various replies to this thread: The users/admins would be the ones who would decide to use dm-multipath. It wouldn't be something that'd be imposed by default. If anything, the all-or-nothing nvme_core.multipath=N would pose a much more serious concern for these array vendors that do have designs to specifically leverage native NVMe multipath. Because if users were to get into the habit of setting that on the kernel commandline they'd literally _never_ be able to leverage native NVMe multipathing. We can also add multipath.conf docs (man page, etc) that caution admins to consult their array vendors about whether using dm-multipath is to be avoided, etc. Again, this is opt-in, so on a upstream Linux kernel level the default of enabling native NVMe multipath stands (provided CONFIG_NVME_MULTIPATH is configured). Not seeing why there is so much angst and concern about offering this flexibility via opt-in but I'm also glad we're having this discussion to have our eyes wide open. Mike
