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

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

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?

> 
>>
>>  src/PVE/Storage/LvmThinPlugin.pm | 18 +++++++++++++++++-
>>  1 file changed, 17 insertions(+), 1 deletion(-)
>>
>> diff --git a/src/PVE/Storage/LvmThinPlugin.pm b/src/PVE/Storage/LvmThinPlugin.pm
>> index 49a4dcb..3f75ba1 100644
>> --- a/src/PVE/Storage/LvmThinPlugin.pm
>> +++ b/src/PVE/Storage/LvmThinPlugin.pm
>> @@ -82,6 +82,19 @@ sub filesystem_path {
>>      return wantarray ? ($path, $vmid, $vtype) : $path;
>>  }
>>  
>> +# lvcreate refuses --setautoactivation for thin volumes, so set it via lvchange
>> +my $set_lv_autoactivation = sub {
>> +    my ($vg, $lv, $autoactivation) = @_;
>> +
>> +    my $cmd = [
>> +	'/sbin/lvchange',
>> +	'--setautoactivation', $autoactivation ? 'y' : 'n',
>> +	"$vg/$lv"
>> +    ];
>> +    eval { run_command($cmd); };
>> +    warn "could not set autoactivation: $@" if $@;
>> +};
>> +
>>  sub alloc_image {
>>      my ($class, $storeid, $scfg, $vmid, $fmt, $name, $size) = @_;
>>  
>> @@ -103,6 +116,7 @@ sub alloc_image {
>>  	       '--thinpool', "$vg/$scfg->{thinpool}" ];
>>  
>>      run_command($cmd, errmsg => "lvcreate '$vg/$name' error");
>> +    $set_lv_autoactivation->($vg, $name, 0);
>>  
>>      return $name;
>>  }
>> @@ -283,6 +297,7 @@ sub clone_image {
>>  
>>      my $cmd = ['/sbin/lvcreate', '-n', $name, '-prw', '-kn', '-s', $lv];
>>      run_command($cmd, errmsg => "clone image '$lv' error");
>> +    $set_lv_autoactivation->($vg, $name, 0);
>>  
>>      return $name;
>>  }
>> @@ -332,7 +347,7 @@ sub volume_snapshot {
>>  
>>      my $cmd = ['/sbin/lvcreate', '-n', $snapvol, '-pr', '-s', "$vg/$volname"];
>>      run_command($cmd, errmsg => "lvcreate snapshot '$vg/$snapvol' error");
>> -
>> +    # disabling autoactivation not needed, as -s defaults to --setautoactivationskip y
>>  }
>>  
>>  sub volume_snapshot_rollback {
>> @@ -346,6 +361,7 @@ sub volume_snapshot_rollback {
>>  
>>      $cmd = ['/sbin/lvcreate', '-kn', '-n', $volname, '-s', "$vg/$snapvol"];
>>      run_command($cmd, errmsg => "lvm rollback '$vg/$snapvol' error");
>> +    $set_lv_autoactivation->($vg, $volname, 0);
>>  }
>>  
>>  sub volume_snapshot_delete {
> 

[1]
https://gitlab.com/lvmteam/lvm2/-/commit/0a28e3c44b05470061f15516e1c89a84fa2e8569



_______________________________________________
pve-devel mailing list
pve-devel@lists.proxmox.com
https://lists.proxmox.com/cgi-bin/mailman/listinfo/pve-devel