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What is backup, and why does the 3-2-1 rule matter?

Backup is your insurance against data loss, ransomware and mistakes. See what a professional backup solution includes, and why the 3-2-1 rule is the standard.

In short

Backup is a copy of your data, stored separately from the original, so you can restore files, emails and systems after ransomware, deletion, hardware failure or human error.

For Danish SMBs, backup is the last line of defence: when everything else fails, the backup determines whether an outage costs hours or weeks. A professional backup solution follows the 3-2-1 rule (three copies of your data, on two different types of media, with at least one stored offsite) and is today often supplemented with an immutable copy that attackers cannot encrypt or delete.

Remember too that Microsoft 365 is not automatically backed up; Microsoft runs the platform, but the responsibility for your data is your own. Finally, backups must be tested regularly, because a backup you have never restored from is only a hope. MI Support IT designs, operates and monitors backup solutions for Danish businesses, including backup of Microsoft 365 and scheduled restore tests.

Back to the glossary

What is backup, and why does the 3-2-1 rule matter?

Backup is a copy of your data (files, emails, databases and entire systems), stored separately from the original, so you can restore everything after ransomware, accidental deletion, hardware failure or fire. A backup solution is, in other words, your insurance against data loss: it determines whether an outage costs an hour or a week.

The Danish Centre for Cyber Security consistently highlights backup as one of the most important defences against ransomware, precisely because modern attackers deliberately go after encrypting or deleting the backup copies first.

What is the 3-2-1 rule?

3-2-1 backup is the industry's rule of thumb for a robust solution:

  • 3 copies of your data: the original plus at least two backups.
  • 2 different media: for example local disk and cloud backup.
  • 1 copy offsite: physically or logically separated from your own network.

Today the rule is often extended with a fourth element: at least one immutable or offline copy that neither attackers nor administrators can change or delete. That is the copy that saves you when ransomware has got hold of everything else, including the backups that sat on the network.

Does Microsoft 365 need backing up? (Yes, here is why)

Many assume that data in Microsoft 365 (formerly Office 365) is automatically protected. But Microsoft operates under a shared responsibility model: Microsoft guarantees the operation of the platform, but the responsibility for your data lies with you. Recycle bins and version history have fixed time limits, so a deleted mailbox or an encrypted SharePoint library is not necessarily recoverable after a few weeks.

A dedicated backup of Microsoft 365 stores email, OneDrive, SharePoint and Teams data independently of Microsoft's own limits, with long retention and fast restore right down to individual files and individual emails.

How often should backups run?

The answer depends on your RPO (Recovery Point Objective): how many hours of work can you afford to lose? If finance and orders run in real time, critical systems may need protecting every hour; for file archives, a day may be enough. RPO and its sibling RTO are the cornerstones of your disaster recovery plan, and backup frequency should always be set based on them, not on whatever the software happens to be configured to.

Backup vs. synchronisation (OneDrive is not backup)

OneDrive, Dropbox and similar services synchronise: they mirror changes across devices. If a file is encrypted by ransomware or deleted by mistake, the damage is synchronised immediately to all copies. Version history can help in individual cases, but it is time-limited and not built to restore an entire company. Synchronisation gives you availability; backup gives you recovery. You need both, but they cannot replace each other.

How MI Support IT can help

MI Support IT delivers backup solutions as a complete, monitored service: 3-2-1 architecture with immutable copies, backup of Microsoft 365 and scheduled, documented restore tests. We connect the backup to your IT contingency plan, so you know exactly how quickly you will be up and running again. Contact us for a review of your current backup.

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