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

[Martin Wilck]

On Fri, 2021-03-26 at 19:10 +0100, Xose Vazquez Perez wrote:
> 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.

Some users are like that, sure. But if that was generally true, we
wouldn't need to adapt our defaults, because everyone would copy the
configs from the vendor manuals.

> 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.

The problem is that the prioritizer was explicitly set to "alua".
Therefore multipathd warns, because the configured setting couldn't be
applied. We could just drop that line, alua would still be selected by
the autodetection if it was supported, and the message wouldn't be
printed any more otherwise. Setting "multibus" explicitly isn't
necessary.

Can we agree on that?

> 
> 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.
> 

That would be for Ben to fix ;-)

Regards
Martin