[linux-lvm] discussion about activation/auto_activation_volume_list

[Gang He]

On 11/18/2020 12:17 AM, David Teigland wrote:
> On Tue, Nov 17, 2020 at 04:00:10PM +0800, heming.zhao at suse.com wrote:
>> Hello LVM-maintainers,
>>
>> Currently activation/auto_activation_volume_list is not enable and it does the default behavior:
>>    pvscan will activate all the devices on booting.
>>
>> This rule will trigger a clumsy process in HA (corosync+pacemaker stack) env.
>>
>> ## let me show the scenario:
>>
>> 2 nodes (A & B) share a disk, and using systemid to manage vg/lv on this shared disk.
>> (keep the activation/auto_activation_volume_list default style: comment out this cfg item)
>>
>> (below steps come from resource-agent LVM-active script)
>> 1. Node A own & active shared vg/lv, node B standby status.
>> 2. A reboot, B detect & wait for A rejoined cluster.
>> 3. because systemid doesn't be changed, lvm2-pvscan at .service will active the vg/lv on A during booting.
>> 4. A finishes reboot, B starts to switch systemid & active shared vg/lv.
>> 5. on B, pacemaker detects lvm resource is running on both nodes.
>> 6. on B, pacemaker restarts lvm resource and enable it on single node.
>>
>> ## rootcause:
>>
>> we can see step 3,4,5 is useless if step 3 is non-existent.
>> So the rootcause is step <3>: node A auto activate shared vg/lv.
> 
> I believe there's an assumption that the system or a user will not
> activate LVs that are managed by the cluster, i.e. only LVM-activate will
> activate LVs managed by the cluster.  Perhaps we could make some attempt
> to enforce that, or at least make sure the instructions for LVM-activate
> make it clear what to do.
> 
>> ## discussion (how to fix):
>>
>> Could activation/auto_activation_volume_list support a new symbol/function like "!".
>> e.g.
>> auto_activation_volume_list = [ "!vg1", "!vg2/lvol1" ]
>> the '!' means lvm absolutely doesn't active this vg1 & vg2/lvol1 automatically.
>>
>> my question:
>> Does it acceptable for LVM2 adding this new function?
> 
> auto_activation_volume_list is difficult to use IMO, and I don't think
> many people use it.  Your suggestion sounds reasonable, but I've wondered
> if autoactivation should be a property set on the VG or LV itself (i.e.
> in the metadata)?  The "activationskip" flag is a possible way to handle
> the unwanted autoactivation, and also seems to justify the idea of making
> autoactivation a similar flag.
I prefer to use a metadata flag for each VG or LV to skip auto-activation.
Otherwise, it is not easy for the pacemaker cluster to manager a local 
VG(e.g. local or systemid type) in a cluster via active-passive mode.

Thanks
Gang

> 
> Dave
> 
> 
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