The pattern repeats. The contracts, the payroll, the customer list and the year's invoices exist in one extra place: a drive in a desk, a laptop that goes home at night, a folder somebody copies to a USB stick when they remember. It feels like a backup because there is a second copy of the file.
It fails in four ordinary ways rather than one dramatic one. The drive breaks or is lost, and years of trading history go with it. Ransomware encrypts the machine and the attached drive together, because the backup was plugged in at the time. Nobody can say which of five similarly named folders is current. And the one person who understands the arrangement is away the week it matters.
A real arrangement has three properties. It runs without anyone remembering to start it. It keeps a copy somewhere the original cannot reach, so a single bad event cannot take both. And somebody restores from it on a schedule, to prove that what comes back is complete and current.
The third is the one that gets skipped, and it is the only one that turns a folder into a recovery plan. Until a restore has actually been done, the backup is a belief rather than a fact.
So the scoping question is not how much storage you have. It is how long the business can be stopped, and how much work you can afford to lose. Answer those two and the design follows - then we test the restore on a date in the calendar, while nothing is on fire.