[pve-devel] [PATCH storage 0/2] Fix #2046 and disksize-mismatch with shared LVM

[Alwin Antreich]

On Fri, Jan 04, 2019 at 02:06:23PM +0100, Stoiko Ivanov wrote:
> The issue was observed recently and can lead to potential dataloss. When using
> a shared LVM storage (e.g. over iSCSI) in a clustered setup only the node, where
> a guest is active notices the size change upon disk-resize (lvextend/lvreduce).
> 
> LVM's metadata gets updated on all nodes eventually (the latest when pvestatd
> runs and lists all LVM-volumes (lvs/vgs update the metadata), however the
> device-files (/dev/$vg/$lv) on all nodes, where the guest is not actively
> running do not notice the change.
> 
> Steps to reproduce an I/O error:
> * create a qemu-guest with a disk backed by a shared LVM storage
> * create a filesystem on that disk and fill it to 100%
> * resize the disk/filesystem
> * put some more data on the filesystem
> * migrate the guest to another node
> * try reading past the initial disksize
> 
> The second patch fixes the size-mismatch by running `lvchange --refresh`
> whenever we activate a volume with LVM and should fix the critical issue
> 
> The first patch introduces a direct implementation of volume_size_info to the
> LVMPlugin.pm, reading the volume size via `lvs`, instead of falling back to
> `qemu-img info` from Plugin.pm.
> While this should always yield the same output after the second patch on the
> node where a guest is currently running, there still might be a mismatch when
> the LV is active (e.g. after a fresh boot) on a node, and gets resized on
> another node.
I faintly recall, that there was a discussion offline about changing the
activation of LVs, especially for booting. Something similar to, 'we
activate LVs only if we need them on the specific node'.