The **[[3-2-1 Backup Strategy]]** is a simple [[Redundancy]] technique to insure against the loss of digital data: Three copies of your data, in two different media, with one copy always kept off-site. ^about These are minimum numbers; each can of course be greater for increased redundancy. - **Three** reasonably accurate **copies** of your data, which includes your production or 'live' dataset - **Two** different **media** [physical storage] types, such as different devices, hard drives, cloud services, etc - **One** always kept **off-site**, which is often a cloud service or self-hosted solution in another location Key risks mitigated for each stage include: - Multiple **copies** insures against outright direct loss or damage to your production data - Multiple **media** insures against the failure of single device, device type, or service - Multiple **locations** insures against the compromise or inaccessibility of any single geographical location **Automatic cloud sync** services **do not count** as a backup method: - While arguably satisfying as 'one of each', the coupled / automatic synchronisation nature of such services exposes your system to the risk of loss or damage propagating 'through' your copies. - For example, unintentional deletion of production data will cascade the deletion of the same data in your cloud instance. Without granular version control and timely intervention, this directly couples any loss of your production data with the loss of your 'backup'. - Similarly, a corruption in the cloud instance may erroneously send destructive updates to your production copy, in which case not even server-side version control is likely to provide recourse.