[DRBD-user] no sync within VM with Xen

[Clément Février]

Hello,

I run into a problem. I have two node with Ubuntu, LVM2, DRBD 8.4 and
Xen. I set up a Logical Volume with DRBD and it seems to work:
On the primary node (named server),
% cat /proc/drbd
version: 8.4.5 (api:1/proto:86-101)
srcversion: 5A4F43804B37BB28FCB1F47
 0: cs:Connected ro:Primary/Secondary ds:UpToDate/UpToDate C r-----
    ns:4259836 nr:8 dw:212 dr:4269307 al:4 bm:0 lo:0 pe:0 ua:0 ap:0 ep:1
wo:f oos:0
and on the secondary node (server2),
% cat /proc/drbd
version: 8.4.5 (api:1/proto:86-101)
srcversion: D496E56BBEBA8B1339BB34A
 0: cs:Connected ro:Secondary/Primary ds:UpToDate/UpToDate C r-----
    ns:8 nr:4259836 dw:4259844 dr:1645 al:1 bm:0 lo:0 pe:0 ua:0 ap:0
ep:1 wo:f oos:0

So everything looks fine. I made an initial sync between nodes. If I
mount the partition /deb/drbd0 on the primary node and make changes, it
is sync properly (checked by umnounting on server, switching to
secondary, setting primary on server2, then mounting the partition).

This partition is actually the root of a VM. If I launch the VM, make
some changes, stop the VM, and mounting the partition on the other node,
then I can see that the partition is unchanged, ie in the state before
the modifications within the VM.

Is there a specific configuration in Xen or DRBD to make?
What am I missing?

Thank you in advance for your help.
Cheers,
Clèm