5 million drivers are online (assume this holds all day, for simplicity). Each phone sends a location update every 3 seconds; an update is 50 bytes (driver_id, lat, lng, timestamp).
Use: 1 day = 86,400 sec ≈ 10^5 sec. Powers of 10: 1 KB = 10^3 B, 1 MB = 10^6 B, 1 GB = 10^9 B, 1 TB = 10^12 B, 1 PB = 10^15 B.
Compute update QPS, daily update count, and one day of raw location storage.