[dm-devel] [PATCH] multipath-tools: convert back HUAWEI/XSG1 to multibus

[Xose Vazquez Perez]

On 3/26/21 6:24 PM, Martin Wilck wrote:

> Forgive me if I'm missing something here, but what is this good for?
> multipathd detects ALUA support by default.
> 
>   1 if the device doesn't support ALUA, it falls back to "const" anyway,
>     in which case "group_by_prio" degenerates to "multibus" - which is
>     exactly what this patch does;
>   2 if the device supports ALUA, but returns the same ALUA state for
>     all ports, again "group_by_prio" degenerates to "multibus";
>   3 if the device supports ALUA and returns different states for
>     different ports, "group_by_prio" is the best bet anyway.
> 
> So why not just use "group_by_prio"?
You are right, but:

1.- It's the official vendor recommendation, and people trust it blindly
     above the multipath-tools setting. Sad but true.
     So it's going to be manually replaced by the vendor's config.

2.- It generates an awful warning:

     [This is SLES 12SP5 with 4.12.14-122.54-default on x86_64
     and multipath-tools-0.7.9+195+suse.16740c5-3.6.1.x86_64]

# multipath -ll

Mar 26 18:34:46 | sdi: prio = const (setting: emergency fallback - alua failed)
Mar 26 18:34:46 | sdj: prio = const (setting: emergency fallback - alua failed)
Mar 26 18:34:46 | sdk: prio = const (setting: emergency fallback - alua failed)
Mar 26 18:34:46 | sdl: prio = const (setting: emergency fallback - alua failed)
36a35324100e5x5d408d0526600000001 dm-1 HUAWEI,XSG1
size=10G features='0' hwhandler='0' wp=rw
`-+- policy='service-time 0' prio=1 status=enabled
   |- 0:0:4:1 sdi 8:128 active ready running
   |- 0:0:5:1 sdj 8:144 active ready running
   |- 1:0:4:1 sdk 8:160 active ready running
   `- 1:0:5:1 sdl 8:176 active ready running

     No nice, mainly for people without knowledge of mpt internals.

3.- The LUN is blacklisted by Fedora and derivatives(RHEL,CentOS,Oracle,...)
     And the installation program is unable to see it, this involves manual intervention.
     See page 76 of the OceanStor RHEL Guide.