A time series system is updated using a data-verification system. The aggregation system may include one or more aggregators. When an upgrade is appropriate, a shadow aggregator may be added to the set of active aggregators. Metrics are provided from one or more collectors to an active aggregator. The shadow aggregator may receive the metrics intended for a particular aggregator, process the metric, and then pass the metric to the intended aggregator for processing. After a period of time, the shadow aggregator data is verified against the intended aggregator data. If the shadow aggregator data is verified, the shadow aggregator becomes an active aggregator and processes data as normal.