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

[Stoiko Ivanov]

On Fri, 4 Jan 2019 14:12:23 +0100
Alwin Antreich <a.antreich at proxmox.com> wrote:

> 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'.

Could make sense in general. However the volumes might get activated by
some external invocation nonetheless (e.g. running `vgchange -ay`) -
then the refresh is still necessary.

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