Re: [pve-devel] [PATCH pve-storage v3 3/3] lvmthin: disable autoactivation for new logical volumes

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

On 27/06/2025 10:14, Fabian Grünbichler wrote:
> 
>> Friedrich Weber <f.weber@proxmox.com> hat am 23.06.2025 11:25 CEST geschrieben:
>>
>>  
>> On 10/06/2025 17:00, Michael Köppl wrote:
>>> On 4/29/25 13:36, Friedrich Weber wrote:
>>>> When discovering a new volume group (VG), for example on boot, LVM
>>>> triggers autoactivation. With the default settings, this activates all
>>>> logical volumes (LVs) in the VG. Activating an LV creates a
>>>> device-mapper device and a block device under /dev/mapper.
>>>>
>>>> Autoactivation is problematic for shared LVM storages, see #4997 [1].
>>>> For the inherently local LVM-thin storage it is less problematic, but
>>>> it still makes sense to avoid unnecessarily activating LVs and thus
>>>> making them visible on the host at boot.
>>>>
>>>> Hence, disable autoactivation after creating new LVs. As lvcreate
>>>> doesn't accept the --setautoactivation flag for thin LVs, this is done
>>>> with an additional lvchange command. With this setting, LVM
>>>> autoactivation will not activate these LVs, and the storage stack will
>>>> take care of activating/deactivating LVs when needed.
>>>>
>>>> [1] https://bugzilla.proxmox.com/show_bug.cgi?id=4997
>>>>
>>>> Signed-off-by: Friedrich Weber <f.weber@proxmox.com>
>>>> ---
>>>>
>>>> Notes:
>>>>     - would be great to get your opinion on whether we should consider
>>>>       LVM-thin storages in this series or not.
>>>>     
>>>>     - passing --setautoactivation n to lvcreate for a thin volume says:
>>>>     
>>>>         Option --setautoactivation is unsupported with thins.
>>>>     
>>>>       But lvchange --setautoactivation seems to work on thin LVs, so the
>>>>       fact that lvcreate doesn't accept it may be a bug. I reported it
>>>>       upstream [1].
>>>>     
>>>>     new in v3
>>>>     
>>>>     [1] https://gitlab.com/lvmteam/lvm2/-/issues/32
>>>
>>> Since the upstream issue has not been addressed yet and the change to
>>> LVM-thin does, AFAICT, not mitigate problems like in #4997 (or am I
>>> missing something here?), but is mostly done to streamline behavior,
>>> could the changes for LVM-thin be held back until it's clear that
>>> lvcreate not supporting --setautoactivation for LVM-thin is not on purpose?
>>
>> Good point. I agree disabling autoactivation isn't as important for
>> LVM-thin as it is for LVM-thick, though it's preferable also here that
>> VM disks are not always active on the host, but only activated on-demand
>> by our storage stack.
>>
>> From looking at the lvm2 commit introducing `--setautoactivation` [1]
>> the omission of --setautoactivation for thin LVs doesn't seem
>> intentional to me (maybe it was just forgotten to add to
>> LVCREATE_ARGS?), but I can't be 100% sure either.
>>
>> The problem with holding back the change for LVM-thin is that we also
>> need a way to update already-existing LVs, and the 8->9 bump is a good
>> opportunity to do so via pve8to9.
>>
>> @Fabian, what do you think?
> 
> it seems very likely this was by accident, and not by design.
> 
> maybe opening an MR fixing it in addition to the issue gets
> more upstream attention?

Good point, thanks. I opened a MR upstream:
https://gitlab.com/lvmteam/lvm2/-/merge_requests/31


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