There is exactly one way to know: restore one and look at the result. Everything else, the green tick in the dashboard, the nightly job that reports success, the reassuring line in the hosting contract, is evidence that a file was written somewhere, not that your site can come back from it. Backups fail silently in boring ways: the database dump that excludes a table, the media folder nobody added to the job, the retention policy that quietly deleted the copy you needed. On sites I host, backups are verified by performing test restores and checking the restored site actually works. If your current supplier cannot tell you when they last restored a backup of your site, you do not have backups. You have files.
Every hosting company says it does backups, and nearly all of them are telling the truth about the first half of the job: something runs nightly and writes files somewhere. The half that matters, whether those files can be turned back into your working website, is tested by almost nobody, because testing costs effort and failure is invisible until the day it is everything.
An Umbraco site is not one thing. It is a database, a media library, application code, configuration and often a search index, and a restore needs a consistent set of all of them. The classic silent failures are a backup job set up before the media library moved, a connection string that points a restored site at the live database, or a dump that has been failing since a password change and reporting success anyway. None of these announce themselves. All of them are found in thirty minutes by doing one real test restore.
On my managed hosting, backups are verified by test restores: the backup is restored and the result is checked as a functioning site, not assumed from a log line. It is unglamorous work, which is why it gets skipped everywhere it is nobody's explicit job.
Ask three things: when did you last restore a backup of my site, how long did it take, and what did you find? A good supplier answers with dates. A vague answer means your disaster recovery plan is a wish. If the answers worry you, my support plans can include putting real recovery testing around a site wherever it currently lives.
Tell me what you're working on and I'll come back within one working day.
A specialist Umbraco developer offering freelance / contract services to a wide variety of clients across the UK
Maesgwyn, 3 Claremont rd,
Llandudno, North Wales, LL30 2UF