[Lsf-pc] [LSF/MM/BPF TOPIC] Native SCSI multipath support

[John Garry]

On 18/02/2026 07:35, Hannes Reinecke wrote:
> On 2/18/26 03:39, Martin K. Petersen wrote:
>>
>> Keith,
>>
>>> For nvme, we can detect if a device is multipath capable.
>>
>> Yep. Same with SCSI...
>>
> And that's how we handle things currently. We've learned from long and 
> painful experiences that there is _NO_ way to automatically figure out
> if a device is multipathed. That will always be an admin decision, so
> there needs to be an opt-in mechanism.
> And that needs to be set _prior_ to probing.
> And you need a driver-specific opt-out, to disable all devices from
> this driver for multipathing (UFS, USB, ATA, you name it).
> 
> Once you have that you can declare all ALUA capable devices with
> a VPD page 83 device identifier as multipathed. Irrespective of
> how many paths will show up.

What I am going to post introduces two mod params.

scsi_multipath.mulitpath and .enable_always

Any scsi device gets multipath treatment when either:

a. .mulitpath enabled and ALUA supported (scsi_device_tpgs() non-zero) 
and unique ID from VPD page 83

b. .enable_always enabled and unique ID from VPD page 83

And all of this will need a new SCSI MULTIPATH config option enabled.

NVMe host driver has similar params.