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    SubjectRe: [PATCH 0/3] Provide more fine grained control over multipathing
    On Mon, 28 May 2018 23:02:36 -0400
    Mike Snitzer <snitzer@redhat.com> wrote:

    > On Mon, May 28 2018 at 9:19pm -0400,
    > Martin K. Petersen <martin.petersen@oracle.com> wrote:
    >
    > >
    > > Mike,
    > >
    > > I understand and appreciate your position but I still don't think
    > > the arguments for enabling DM multipath are sufficiently
    > > compelling. The whole point of ANA is for things to be plug and
    > > play without any admin intervention whatsoever.
    > >
    > > I also think we're getting ahead of ourselves a bit. The assumption
    > > seems to be that NVMe ANA devices are going to be broken--or that
    > > they will require the same amount of tweaking as SCSI devices--and
    > > therefore DM multipath support is inevitable. However, I'm not sure
    > > that will be the case.
    > >
    > > > Thing is you really don't get to dictate that to the industry.
    > > > Sorry.
    > >
    > > We are in the fortunate position of being able to influence how the
    > > spec is written. It's a great opportunity to fix the mistakes of
    > > the past in SCSI. And to encourage the industry to ship products
    > > that don't need the current level of manual configuration and
    > > complex management.
    > >
    > > So I am in favor of Johannes' patches *if* we get to the point
    > > where a Plan B is needed. But I am not entirely convinced that's
    > > the case just yet. Let's see some more ANA devices first. And once
    > > we do, we are also in a position where we can put some pressure on
    > > the vendors to either amend the specification or fix their
    > > implementations to work with ANA.
    >
    > ANA really isn't a motivating factor for whether or not to apply this
    > patch. So no, I don't have any interest in waiting to apply it.
    >
    Correct. That patch is _not_ to work around any perceived incompability
    on the OS side.
    The patch is primarily to give _admins_ a choice.
    Some installations like hosting providers etc are running quite complex
    scenarios, most of which are highly automated.
    So for those there is a real benefit to be able to use dm-multipathing
    for NVMe; they are totally fine with having a performance impact if
    they can avoid to rewrite their infrastructure.

    Cheers,

    Hannes

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