Aha! And it turns out that upgrading and rebooting the storage servers on tahoebs5 don't change the failure. See ticket #748. Regards, Zooko tickets mentioned in this mail: http://allmydata.org/trac/tahoe/ticket/748 # Exception: <class 'allmydata.mutable.common.UncoordinatedWriteError'> when trying to create directory on testgrid