Everyone agrees that backups must be sent off site in order to protect your data from large disasters such as fire, earthquake, tornado, hurricane or flood.
If you store your backups in the same place you create your data, your backups will get destroyed along with your data. If you put them somewhere else, you at least have a chance at restoring data when the worst happens. The method you choose to get the data to another location will determine the likelihood and cost of such an event. Here are the various ways that people get data their off-site.
Original tape given to a man in a van
The oldest method is to hand to a “man in a van” the original tapes that contain your backup, but it comes with a number of downsides. Because you are using your original backup tape, you have two choices: use the latest tape or an older tape. If you use the latest tape, you will be able to restore from your most recent backups if you have a disaster. This would allow you to meet a lower recovery point objective, or RPO.
On the other hand, you want to use an older tape because sending last night's backup off-site would make it unavailable for day-to-day operational restores. Since operational restores are the ones you do most often, this is the most significant downside of this method. Any recovery time objective (RTO) for operation recoveries would have to account for the amount of time it takes to get the tape back on site.
Another downside is the risk of physically shipping media. Unless all of your backups are encrypted as they are being written to tape, the loss of any of your backups might need to be reported, especially if you are subject to data-privacy laws or regulations. Any time you hand tapes to a man in a van, you are opening yourself up to risk.
The main advantages of this method are simplicity and a reduction in media costs. The Catch-22 decision of having to decide between a good disastar-recovery RPO and a good operational recovery RTO is a significant one, as is the risk of lost data by physically shifting media – especially important because the tapes in question are the only copy of your backup.
Copy of backup to a man in a van
The next method is very similar to the first, but instead of sending your original off-site, you send a copy. This addresses many of the previously mentioned downsides, as it allows you to send the latest backup off-site without affecting the RTO of operational recoveries or placing the only copy of your latest backup at risk. You do still have the risk of lost data unless you encrypt your backups, though.
The on-site backup used for operational restores could be disk or tape. You would first send your backups to disk, then copy them to tape, then hand the copied tape to the man in a van.
Disk and replication
Replication of backups is possible if backups are deduplicated, and you have sufficient bandwidth. Deduplication can reduce by two orders of magnitude the size of data that needs to be replicated.
Thanks to W. Curtis Preston (see source)