HBase is used at China Telecom for various applications including persistence for streaming jobs, online reading and writing, and as a data store for their core system. They operate several HBase clusters storing over 500 TB of data ingesting 1 TB per day. They monitor HBase using Ganglia for basic metrics and Zabbix for critical alerts. When issues arise, such as a system hang, they investigate debug cases and perform optimizations like changing the garbage collector from CMS to G1 and implementing read/write splitting.