The agents collect operational data from the storage servers and transfer it to data collection servers. The system detected the stuck servers (a hard failure), and failed over to healthy servers, but there were so many stuck servers that the healthy servers couldn’t keep up, and also became stuck. It happened because of the co-incidence of a hardware failure in one component of the monitoring subsystem (a data collection server) and a software bug in another component of the monitoring subsystem (data collection agent).