100M active time series is good information, but what's the data rate for each time series it can handle? One update per minute or 10 per second? There's a factor of 600 difference there. Neither is obviously insanely the wrong update rate.

scrape interval is 15s and sustained ingestion we have seen is ~3M samples/sec that is ~300 TB/day of raw ingest payload, when stored on object store as parquet, the data gets compressed to 99% which makes it 3 TB/day. The 100M figure is total unique series seen over time. For a sense of per metric cardinality, one metric that has the highest cardinality label (2.5 M distinct values) shows ~6M active series per hour.