[DRBD-user] DRBD 8 - 9 Upgrade Planning

[Dingwall, James]

Hi,

We are planning an upgrade from drbd 8.4 to 9.1 at the moment.  Our usage of drbd is backing storage for virtual machines running on Xen where we support live migration by temporarily running dual primary when required.  In a typical upgrade we change one side of the cluster and then wait a few days before completing the second side.  We have read through section 4.7 of the user guide relating to upgrading clusters but didn't see any information on the behaviour we should expect while the cluster is running mixed versions.  The closest statement we have found (which we don't read as authoratitive as it isn't a linbit resource) is [1]:

"a drbd node on 8.4 can replicate to a node with drbd 9.0 , BUT NOT THE OPPOSITE"

We are building a test cluster at the moment to make our own checks but it would be very useful if we knew what we should expect.

Thanks,
James

[1] https://askubuntu.com/questions/1235614/upgrading-drbd8-to-drbd9