Which type of backup medium is most effective against catastrophic natural events?

The most effective backup medium against catastrophic natural events is an offsite repository. This is because an offsite repository stores data in a different physical location from where the primary data is held. In the event of a natural disaster, such as a flood, fire, or earthquake, if the primary site is affected, the data stored offsite remains safe and accessible.

While an online backup solution can also be effective, it typically requires a stable internet connection and may not provide the same immediacy in access compared to having data stored physically offsite. External hard drives and onsite tape backups are vulnerable to the same disasters that can affect the primary data center. They would likely be damaged or destroyed if those environments become compromised. Thus, an offsite repository is optimal for ensuring data resilience against such catastrophic events.