[pve-devel] [PATCH manager/storage v4 0/5] fix #4997: lvm, lvm-thin: avoid autoactivating LVs

[Friedrich Weber]

# Summary

With default settings, LVM autoactivates LVs when it sees a new VG, e.g. after
boot or iSCSI login. In a cluster with guest disks on a shared LVM VG (e.g. on
top of iSCSI/Fibre Channel (FC)/direct-attached SAS), this can indirectly cause
guest creation or migration to fail. See bug #4997 [1] and patch #1 for
details.

The primary goal of this series is to avoid autoactivating thick LVs that hold
guest disks in order to fix #4997. For this, it patches the LVM storage plugin
to create new LVs with autoactivation disabled, and implements a pve8to9 check
and subcommand to disable autoactivation on existing LVs (see below for
details).

The series does the same for LVM-thin storages. While LVM-thin storages are
inherently local and cannot run into #4997, it can still make sense to avoid
unnecessarily activating thin LVs at boot.

# Why not before PVE 9

As discussed in v2, we should only apply this series for PVE 9, as we can be
sure all nodes are running at least PVE 8 then. Here is why we couldn't apply
it for PVE 8 already.

PVE 7/Bullseye's LVM does not know `--setautoactivation`. A user upgrading from
PVE 7 will temporarily have a mixed 7/8 cluster. Once this series is applied,
the PVE 8 nodes will create new LVs with `--setautoactivation n`, which the PVE
7 nodes do not know. In my tests, the PVE 7 nodes can read/interact with such
LVs just fine, *but*: As soon as a PVE 7 node creates a new (unrelated) LV, the
`--setautoactivation n` flag is reset to default `y` on *all* LVs of the VG. I
presume this is because creating a new LV rewrites metadata, and the PVE 7 LVM
doesn't write out the `--setautoactivation n` flag. I imagine (have not tested)
this will cause problems on a mixed cluster.

# pve8to9 script

As discussed in v2, this series implements

(a) a pve8to9 check to detect thick and thin LVs with autoactivation enabled
(b) a script to disable autoactivation on LVs when needed, intended to be run
    manually by the user during 8->9 upgrade

The question is where to put the script (b). Patch #4 moves the existing checks
from `pve8to9` to `pve8to9 checklist`, to be able to implement (b) as a new
subcommand `pve8to9 updatelvm`. I realize this is a huge user-facing change,
and we don't have to go with this approach. It is also incomplete, as patch #5
doesn't update the manpage yet. However, I like about this approach that
pve8to9 bundles "tasks that are related to 8->9 upgrades". If we do decide to
go with this, I can send another patch to update the manpage as well as add
documentation.

# Bonus fix for FC/SAS multipath+LVM issue

As it turns out, this series seems to additionally fix an issue on hosts with
LVM on FC/SAS-attached LUNs *with multipath* where LVM would report "Device
mismatch detected" warnings because the LVs are activated too early in the boot
process before multipath is available. Our current suggested workaround is to
install multipath-tools-boot [2]. With this series applied and when users have
upgraded to 9, this shouldn't be necessary anymore, as LVs are not
auto-activated after boot.

# Interaction with zfs-initramfs

zfs-initramfs used to ship an an initramfs-tools script that unconditionally
activates *all* VGs that are visible at boot time, ignoring the autoactivation
flag. A fix was already applied in v2 [3].

# Patch summary

- Patch #1 makes the LVM plugin create new LVs with `--setautoactivation n`
- Patch #2 makes the LVM-thin plugin disable autoactivation for new LVs
- Patch #3 runs perltidy on pve8to9, can be dropped
- Patch #4 moves pve8to9 checks to a subcommand (see pve8to9 section above)
- Patch #5 adds a pve8to9 subcommand to disable autoactivation
  (see pve8to9 section above)

# Changes since v3

- rebase and run perltidy
- see individual patches for other changes
- @Michael tested+reviewed v3 (thx!), but since there were some code changes,
  I'm not including the trailers here, even though the changes on #1+#2 were
  mostly comments/formatting changes.

# Changes since v2

- drop zfsonlinux patch that was since applied
- add patches for LVM-thin
- add pve8to9 patches

v3: https://lore.proxmox.com/pve-devel/20250429113646.25738-1-f.weber@proxmox.com/
v2: https://lore.proxmox.com/pve-devel/20250307095245.65698-1-f.weber@proxmox.com/
v1: https://lore.proxmox.com/pve-devel/20240111150332.733635-1-f.weber@proxmox.com/

[1] https://bugzilla.proxmox.com/show_bug.cgi?id=4997
[2] https://pve.proxmox.com/mediawiki/index.php?title=Multipath&oldid=12039#%22Device_mismatch_detected%22_warnings
[3] https://lore.proxmox.com/pve-devel/ad4c806c-234a-4949-885d-8bb369860cc0@proxmox.com/

pve-storage:

Friedrich Weber (2):
  fix #4997: lvm: create: disable autoactivation for new logical volumes
  lvmthin: disable autoactivation for new logical volumes

 src/PVE/Storage/LVMPlugin.pm     | 13 ++++++++++++-
 src/PVE/Storage/LvmThinPlugin.pm | 17 ++++++++++++++++-
 2 files changed, 28 insertions(+), 2 deletions(-)


pve-manager:

Friedrich Weber (3):
  pve8to9: run perltidy
  pve8to9: move checklist to dedicated subcommand
  pve8to9: detect and (if requested) disable LVM autoactivation

 PVE/CLI/pve8to9.pm | 178 ++++++++++++++++++++++++++++++++++++++++++++-
 bin/Makefile       |   2 +-
 2 files changed, 175 insertions(+), 5 deletions(-)


Summary over all repositories:
  4 files changed, 203 insertions(+), 7 deletions(-)

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