[pve-devel] [PATCH pve-storage v3 2/3] fix #4997: lvm: create: disable autoactivation for new logical volumes

[Friedrich Weber]

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.

This is not necessarily problematic for local LVM VGs, but it is
problematic for VGs on top of a shared LUN used by multiple cluster
nodes (accessed via e.g. iSCSI/Fibre Channel/direct-attached SAS).

Concretely, in a cluster with a shared LVM VG where an LV is active on
nodes 1 and 2, deleting the LV on node 1 will not clean up the
device-mapper device on node 2. If an LV with the same name is
recreated later, the leftover device-mapper device will cause
activation of that LV on node 2 to fail with:

> device-mapper: create ioctl on [...] failed: Device or resource busy

Hence, certain combinations of guest removal (and thus LV removals)
and node reboots can cause guest creation or VM live migration (which
both entail LV activation) to fail with the above error message for
certain VMIDs, see bug #4997 for more information [1].

To avoid this issue in the future, disable autoactivation when
creating new LVs using the `--setautoactivation` flag. With this
setting, LVM autoactivation will not activate these LVs, and the
storage stack will take care of activating/deactivating the LV on the
correct node when needed.

This additionally fixes an issue with multipath on FC/SAS-attached
LUNs where LVs would be activated too early after boot when multipath
is not yet available, see [3] for more details and current workaround.

The `--setautoactivation` flag was introduced with LVM 2.03.12 [2],
Bookworm/PVE 8 ships 2.03.16.

Note that the flag is only set for newly created LVs, so LVs created
before this patch can still trigger #4997. To avoid this, users will
be advised to run a script to disable autoactivation for existing LVs.

[1] https://bugzilla.proxmox.com/show_bug.cgi?id=4997
[2] https://gitlab.com/lvmteam/lvm2/-/blob/main/WHATS_NEW
[3] https://pve.proxmox.com/mediawiki/index.php?title=Multipath&oldid=12039#FC/SAS-specific_configuration

Signed-off-by: Friedrich Weber <f.weber at proxmox.com>
---

Notes:
    probably need to wait until PVE 9 for applying this, see cover letter
    
    changes since v2:
    - reworded commit message
    
    new in v2

 src/PVE/Storage/LVMPlugin.pm | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/PVE/Storage/LVMPlugin.pm b/src/PVE/Storage/LVMPlugin.pm
index b371b4c..6a22f3e 100644
--- a/src/PVE/Storage/LVMPlugin.pm
+++ b/src/PVE/Storage/LVMPlugin.pm
@@ -352,6 +352,7 @@ sub lvcreate {
 	'--yes',
 	'--size', $size,
 	'--name', $name,
+	'--setautoactivation', 'n',
     ];
     for my $tag (@$tags) {
 	push @$cmd, '--addtag', $tag;
-- 
2.39.5