linux-kernel - Re: [PATCH 0/3] Provide more fine grained control over multipathing

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Date:   Thu, 31 May 2018 18:36:03 +0200
From:   Christoph Hellwig <hch@....de>
To:     Sagi Grimberg <sagi@...mberg.me>
Cc:     Mike Snitzer <snitzer@...hat.com>, Christoph Hellwig <hch@....de>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        Keith Busch <keith.busch@...el.com>,
        Hannes Reinecke <hare@...e.de>,
        Laurence Oberman <loberman@...hat.com>,
        Ewan Milne <emilne@...hat.com>,
        James Smart <james.smart@...adcom.com>,
        Linux Kernel Mailinglist <linux-kernel@...r.kernel.org>,
        Linux NVMe Mailinglist <linux-nvme@...ts.infradead.org>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        Martin George <marting@...app.com>,
        John Meneghini <John.Meneghini@...app.com>
Subject: Re: [PATCH 0/3] Provide more fine grained control over multipathing

On Thu, May 31, 2018 at 11:37:20AM +0300, Sagi Grimberg wrote:
>> 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.
>
> You are referring to an array exposing media via nvmf and scsi
> simultaneously? I'm not sure that there is a clean definition of
> how that is supposed to work (ANA/ALUA, reservations, etc..)

It seems like this isn't what Mike wanted, but I actually got some
requests for limited support for that to do a storage live migration
from a SCSI array to NVMe.  I think it is really sketchy, but if
doable if you are careful enough.  It would use dm-multipath, possibly
even on top of nvme multipathing if we have multiple nvme paths.