After the installation of Update 4, the cluster appears to be in degraded state. All I/O write operations are frozen.
All servers in cluster show a very high load average.
pstorage -c <clustername> top you can see the following message :
MDS WRN Failed to allocate replicas in 2 domain(s), only 1 domain(s) available
Previously, the cluster was configured with high "locality" setting.
Update 4 introduces the division of the cluster into failure domains, and after its installation, high "locality" parameter has been changed to an incorrect "failure-domain" setting :
~# pstorage -c <clustername> get-attr -p / Attributes: replicas=1:1 failure-domain=room <-------------!!!
man pstorage-failure-domain for detailed information.
Configure proper failure-domain parameter, according to documentation.
pstorage -c <clustername> set-attr -R -p / failure-domain=host