Re: [pve-devel] [PATCH storage 0/2] fix #4997: lvm: avoid autoactivating (new) LVs after boot

[Friedrich Weber <f.weber@proxmox.com>]

Thanks for the review!

On 26/01/2024 12:14, Fiona Ebner wrote:
>> Some points to discuss:
>>
>> * Fabian and I discussed whether it may be better to pass `-K` and set the
>>   "activation skip" flag only for LVs on a *shared* LVM storage. But this may
>>   cause issues for users that incorrectly mark an LVM storage as shared, create a
>>   bunch of LVs (with "activation skip" flag), then unset the "shared" flag, and
>>   won't be able to activate LVs afterwards (`lvchange -ay` without `-K` on an LV
>>   with "activation skip" is a noop). What do you think?
>>
> 
> Is there a way to prevent auto-activation on boot for LVs on a shared
> (PVE-managed) LVM storage? Also a breaking change, because users might
> have other LVs on the same storage, but would avoid the need for the
> flag. Not against the current approach, just wondering.

One can also disable autoactivation for a whole VG (i.e., all LVs of
that VG):

	vgchange --setautoactivation n VG

At least in my tests, after setting this no LV in that VG is active
after boot, so this might also solve the problem. I suppose setting this
automatically for existing VGs would be too dangerous (as users might
have other LVs in that VGs). But our LVM storage plugin *could* set this
when creating a new shared VG [1]?

Not sure which option is better, though.

> Guardrails against issues caused by misconfiguration always warrant a
> cost-benefits analysis. What is the cost for also setting the flag for
> LVs on non-shared LVM storages? Or logic needs to be correct either way ;)

AFAICT, setting this LV flag on non-shared LVM storages doesn't have
negative side-effects. I don't think we rely on autoactivation anywhere.
We'd need to take care of passing `-K` for all our `lvchange -ay` calls,
but AFAICT, `lvchange` calls are only done in the LVM/LvmThin plugins in
pve-storage.

[1]
https://git.proxmox.com/?p=pve-storage.git;a=blob;f=src/PVE/Storage/LVMPlugin.pm;h=4b951e7a;hb=8289057e#l94