Plan a backup strategy for your data.
The 3-2-1 rule asks for three copies of your data on two different media with one held offsite, which means total capacity is your data multiplied by the copy count rather than equal to it. Growth compounds, so the plan has to be sized for a year ahead: three percent monthly growth is roughly forty-three percent over twelve months, which is enough to overflow a drive bought to fit today.
Capacity required
Total capacity = primary data x number of copies
Growth and cost
Capacity in 12 months = primary data x (1 + monthly growth) ^ 12 x copies; monthly offsite cost = data x offsite copies x cost per GB
Three copies of the data, stored on at least two different types of media, with at least one copy held offsite. It survives drive failure, device loss and site-level events such as fire or theft.
Only partly. Sync propagates deletion and ransomware encryption to every copy, so a service without versioning or immutable retention is not a backup.