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.
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