Online backup is a low-cost service that copies a person's or a small business's computers to the cloud, with no backup hardware of their own. It is also called consumer cloud backup. These services are sold mainly in the United States, to households, freelancers and small offices, for a fixed monthly or yearly fee in US dollars. In India, most people instead rely on the cloud storage that comes with their phone or their email account.
How does it work? The person installs a small app on each computer. On the first day, the app uploads every file on the computer. For a large drive, this first upload can take days. After that, the app watches for new and changed files, and uploads them every few minutes. Each file is encrypted on the computer before it leaves, which means it is scrambled so that only someone with the right key can read it. Some services let the customer set a private key, so that even the provider cannot read the files.
The service keeps old versions of each file, typically for 30 days or for a year. This matters. If ransomware encrypts the files on the computer, the app uploads the encrypted versions too. But the earlier, clean versions are still in the cloud.
Online backup is not the same as a sync folder, such as the ones that come with an email account. A sync folder makes the same change everywhere. If a file is deleted on the laptop, it is deleted in the cloud as well. A backup keeps the deleted file, so it can still be restored.
Consider a family-run accounting office in Ohio, in the United States, with three desktops and a laptop. Each computer runs the backup app, for a fee of under $10 a month per computer. The first upload of 800 GB takes about a week on the office's internet connection. In April, during the US tax season, one desktop's hard drive fails. The owner needs 300 GB of client tax files back on a new computer. Downloading them would take most of a day. So she orders the files on a hard drive, delivered by courier in two days, and keeps working from the files she downloads first.
The same companies also sell cheap object storage to developers and businesses, priced for each terabyte stored each month. Some antivirus and security suites include a small amount of online backup as well. Larger companies, which need an IT team to manage hundreds of laptops from one screen, buy endpoint backup instead.