NoSQL systems have grown in popularity for storing big data because these systems offer high availability, i.e., Operations with high throughput and low latency. However, metadata in these systems are handled today in ad-hoc ways. We present Wasef, a system that treats metadata in a NoSQL database system, as first-class citizens. Metadata may include information such as: operational history for a database table (e.g., Columns), placement information for ranges of keys, and operational logs for data items (key-value pairs). Wasef allows the NoSQL system to store and query this metadata efficiently. We integrate Wasef into Apache Cassandra, one of the most popular key-value stores. We then implement three important use cases in Cassandra: dropping columns in a flexible manner, verifying data durability during migrational operations such as node decommissioning, and maintaining data provenance. Our experimental evaluation uses AWS EC2 instances and YCSB workloads. Our results show that Wasef: i) scales well with the size of the data and the metadata, ii) minimally affects throughput and operation latencies.