For further info see
https://bugs.launchpad.net/bugs/1251137
Basically it is the same old MySQL story: you upgrade slaves first. So
for the duration of upgrade the cluster must be operated in master-slave
mode.
Notwithstanding the 5.5->5.6 migration challenge, we believe this is our
best release to date, both 5.5 and 5.6.
Thanks,
Alex
--
Alexey Yurchenko,
Codership Oy,
www.codership.com
Skype: alexey.yurchenko, Phone: +358-400-516-011