when one node runs out of disk space memcached goes into pending mode ) and the user can rebalance this node out from the cluster.
Shutting down bucket "default" on 'firstname.lastname@example.org' for server shutdown ns_memcached002 email@example.com 18:48:24 - Tue May 24, 2011
Usage of disk "/" on node "172.16.75.128" is over 100%
if you have two nodes running out of disk space you will not be able to failover those two nodes because failover will timeout.
the workaround is if you have two or more nodes running out of disk space you need to stop membase server on those two nodes and then you can fail over those nodes.