Backup advice tends to be either "just back it up" or a forty-page policy. Between them sits a rule short enough to remember and strict enough to work: three copies of anything that matters, on two different kinds of storage, with one copy somewhere else.
Three copies
The live data, plus two backups. One backup is a single point of failure — the drive fails, the backup job silently stopped in March, the ransomware reached it.
Two kinds of storage
Different media fail differently. A local backup appliance for fast restores and a cloud repository for everything else means no single fault takes out both.
One off-site — and, today, one offline
Fire, flood, theft, and above all ransomware. The modern addition to the rule is that at least one copy must be immutable: unchangeable for a set period, unreachable even to an administrator. That is the copy the intruder cannot delete, and the one you restore from.
The rule nobody writes down
A backup is not a backup until it has been restored. We test restores on a schedule and record the result, so when a customer asks "how long would we be down?" the answer is a number we have measured, not a guess. Boring, weekly, and the reason the worst day ends with a report rather than a ransom.
