What is immutable backup?

As data becomes the heartbeat of business operations, the threats surrounding it are escalating and evolving just as rapidly. Cybercriminals are no longer just stealing or encrypting data — they’re now targeting backup infrastructure itself. By disabling or corrupting backups, threat actors aim to block recovery paths and pressure victims to pay ransoms. That’s why immutable backups — copies of data that cannot be altered or deleted, even by threats like ransomware — have become essential.

Implementing immutable backups is now critical for businesses, their technology partners and managed service providers (MSPs) to ensure recovery remains possible in the face of sophisticated attacks. Immutable backups ensure business continuity, support regulatory compliance and provide a robust defense against advanced threats like ransomware.

In this article, we’ll explore what immutable backups are, how they work, the benefits they deliver and the critical role they play in building a resilient business continuity and disaster recovery (BCDR) strategy.

What are immutable backups?

Immutable backups are copies of data that cannot be modified, overwritten or deleted for a fixed period of time. Once created, these backups remain completely locked, ensuring no changes — whether accidental or malicious — can be made during the retention window. This makes them a powerful line of defense against threats like ransomware and malicious insiders seeking to compromise or erase recovery points.

Immutability is enforced through a combination of software-defined policies and storage platform capabilities, ensuring that backup data stays exactly as it was at the time of creation, regardless of user actions, malware or system errors.

Typically, immutable backups are implemented using:

• Purpose-built backup appliances
• Cloud-based storage solutions
• Hybrid systems that combine on-premises and cloud environments

What is the difference between immutable backup and normal backup?

The key difference between immutable backups and normal backups lies in how the data is protected and controlled.

Normal backups can be modified, overwritten or deleted, either by users, automated systems or malicious actors. While useful for routine recovery, they remain vulnerable to ransomware, accidental deletion or insider tampering. If a threat actor gains access to backup files, they can often erase or encrypt them.

Immutable backups, on the other hand, are locked for a defined retention period. During that time, the data cannot be changed or removed by anyone, not even administrators. This permanent ensures that recovery points remain intact, even in the face of advanced cyberthreats or human error.

To better understand the contrast, here’s a quick side-by-side comparison of immutable backup solutions and normal backups:

Notably, immutable backups are often mistaken for air-gapped backups. While both approaches are designed to protect backup data from tampering, they work in fundamentally different ways and often serve different purposes within a broader data protection strategy.

Immutable backup vs. air gap backup

Immutable backups remain fully accessible and connected to the network, allowing for fast recovery when needed. This ensures continuous protection without sacrificing availability.

In contrast, air-gapped backups rely on isolating the data completely. These backups are stored on systems that are either physically disconnected or logically segmented from production networks. By removing network access entirely, air-gapped backups are shielded from any attack that spreads through the infrastructure, including malware or unauthorized access. However, this also means the backups are not readily available for recovery during a disruption.

In many cases, organizations use both — immutable backups for continuous, fast-access protection and air-gapped backups as an extra layer of defense against highly targeted or advanced attacks.

Why are immutable backups important?

In today’s complex IT environments, protecting data isn’t just about storing it — it’s about preserving its integrity. Immutable backups play a crucial role by ensuring that once data is backed up, it stays in its original, unaltered state for a fixed period. This integrity allows businesses to recover with confidence, even when faced with sophisticated cyberthreats, internal misuse or common human errors.

Resilience from ransomware and cyberattacks

Modern ransomware doesn’t just target live data. It actively seeks out backup systems to encrypt, corrupt or delete recovery points, leaving organizations with no way to restore. Immutable backups stop this by locking backup files so they can’t be altered or erased, even if an attacker gains administrative access. This ensures a clean, recoverable copy of data is always available, helping avoid extended downtime and ransom demands.

Protection from insider threats and unauthorized access

Not all threats come from outside. Malicious insiders, misused credentials or even well-meaning staff can intentionally or accidentally tamper with backup files. Immutable backups eliminate this risk by preventing any changes, regardless of user role or permissions. Even users with high-level access can’t delete or alter the data, adding a powerful layer of protection against internal risks.

Prevention of accidental deletion and corruption

Human error remains one of the most common causes of data loss. A mistyped command, a misconfigured job or a faulty update can corrupt or wipe out critical data in seconds. Immutable backups guard against this by ensuring backup copies can’t be modified or overwritten. This guarantees that a clean, untouched version of the data is always available for recovery, keeping operations running smoothly.

How do immutable backups work?

Immutable backups rely on a set of technical controls that prevent backup data from being modified, deleted or tampered with. These controls are built into the storage infrastructure and the backup management systems, working together to ensure that every backup remains exactly as it was when it was created.

Here’s how immutability is enforced at each layer:

• Immutable storage: At the core of an immutable backup is the use of storage systems designed to prevent changes. These platforms ensure that once data is written, it can’t be altered. Whether deployed on-premises, in the cloud or in hybrid environments, immutable storage provides the foundation for long-term data integrity.
• Write-once, read-many (WORM) technology: WORM technology ensures that data can only be written once and read many times. Once a file is written to WORM storage, it cannot be modified or deleted until its retention period expires. This technology is key to making sure that backup data stays fixed and untouchable, even if an attacker or administrator attempts to alter it.
• Locked retention policies: Administrators define how long backup data should remain immutable by setting retention policies. Once these policies are applied, they cannot be shortened or removed until the set duration is complete. This prevents anyone, including users with elevated access, from bypassing the immutability rules and tampering with stored data.
• Access controls and audit trails: Strong access controls limit who can interact with backup systems, while detailed audit logs track every access attempt and action taken. These controls help prevent unauthorized changes and provide full visibility into who accessed backup data and when. Even in the event of a security breach, the integrity of the backups remains intact and verifiable.

Together, these technologies ensure that immutable backups stay locked, accurate, reliable and ready for recovery whenever they’re needed.

Advantages of immutable backup technology

For businesses and MSPs, the value of immutable backup technology extends far beyond data storage. It directly supports cyber resilience and dependable business continuity by ensuring backup data remains intact, secure and ready for recovery, no matter what. These benefits help reduce downtime, meet compliance mandates and maintain operational confidence during unexpected disruptions.

Recovery confidence

When disaster strikes, recovery speed and reliability are everything. Immutable backups give IT teams the assurance that their recovery points are clean, complete and untouched. Even if ransomware hits or a user mistakenly deletes data, the latest immutable copy is always available.

This consistency directly supports lower recovery point objectives (RPOs), ensuring that businesses can restore to the most recent backup with minimal data loss. For example, an MSP recovering a client’s systems after a ransomware incident can trust that their last immutable backup is safe, verified and ready to restore immediately.

Regulatory compliance

Regulations like the General Data Protection Regulation (GDPR), the Health Insurance Portability and Accountability Act (HIPAA) and the Sarbanes-Oxley Act (SOX) require not only data retention but also proof that data has not been altered or deleted. Immutable backups provide this proof by enforcing unchangeable retention policies and capturing detailed audit trails.

A healthcare provider, for instance, must retain patient records for several years and demonstrate that these records haven’t been tampered with. Immutable storage ensures that archived data remains compliant, secure and accessible for audits or legal inquiries.

Historical data preservation

Some data needs to be preserved not just for disaster recovery but also for historical, legal or analytical purposes. Immutable backups make it possible to maintain accurate long-term records that reflect the original state of the data.

A financial services firm, for example, might need to retain transactional records for regulatory reviews or trend analysis over multiple years. With immutability in place, they can be confident that those records remain unchanged and can be trusted as a reliable source of truth.

What role does backup immutability play in BCDR?

At the core of any business continuity and disaster recovery strategy is a simple goal: recover critical data quickly and accurately so that business operations continue running, no matter the cause of disruption. Whether the threat is ransomware, a system failure or a natural disaster, the ability to bounce back depends on the integrity of backups.

This is where backup immutability becomes a powerful enabler.

Immutable backups ensure that your recovery points are not only available, but verified and untouched. Even if a ransomware attack penetrates deep into your environment, it cannot alter or erase your protected backups. This guarantees access to known-good data, helping teams reduce both recovery time objectives (RTOs) and recovery point objectives.

Immutability also plays a key role in supporting the 3-2-1-1-0 backup strategy — a modern best practice for data protection. According to this approach, you should maintain:

• 3 total copies of your data,
• on 2 different types of media,
• with 1 off-site copy,
• 1 immutable copy,
• and 0 backup recovery errors.

That final “1” and “0” in the rule — representing immutability and recovery verification — are where immutable backups shine. They offer the assurance that one copy of your data is locked, secure and recoverable without corruption or compromise.

Immutable backups are a core pillar for organizations and MSPs building a layered BCDR strategy. They give stakeholders, customers and regulators confidence that recovery is not just possible but dependable.

Want to learn more about the 3-2-1-1-0 strategy and how to implement it effectively? Read our full guide on the 3-2-1-1-0 backup rule.

Keep backups resilient with Datto BCDR

As threats grow more sophisticated, immutable backups have become essential for protecting business-critical data and ensuring reliable recovery. They form the foundation of any solid business continuity and disaster recovery strategy.

Datto delivers this immutability through purpose-built backup appliances and a resilient cloud that safeguards data through multiple security layers. By combining secure on-premises storage with immutable backups in the Datto Cloud, Datto gives businesses and MSPs powerful tools to protect against ransomware, insider threats and other data threats while maintaining fast recovery capabilities.

Here’s how Datto BCDR helps keep your backups resilient and always recoverable:

• Hardened Linux-based appliances: Datto’s hardened on-premises appliances run on Linux, significantly reducing the attack surface compared to Windows-based systems. This adds a critical layer of protection at the hardware level, helping prevent compromise from known exploits.
• Immutable cloud backups: Backups sent to the Datto Cloud are written in a WORM format and stored immutably. They can’t be encrypted or corrupted, making them a reliable last line of defense against ransomware and accidental loss.
• Multiple layers of security: Datto combines multiple layers of security to deliver resilient, tamper-proof backups.
• Enterprise-grade protection: All backups replicated to the Datto Cloud are encrypted with AES-256 encryption — both at rest and in transit — and secured with two-factor authentication (2FA) for portal access.
• Smart file system: Datto uses the Zettabyte File System (ZFS) for backup storage, a robust architecture with built-in integrity checking, copy-on-write snapshots, zero-copy clones, data compression and automatic repair to prevent corruption.
• Cloud Deletion Defense™: Even if agents or backup snapshots are deleted — accidentally or maliciously — they can be recovered quickly and completely.
• Ransomware detection: Every backup is scanned using advanced machine learning algorithms to detect signs of ransomware encryption. If suspicious activity is found, you’re alerted immediately, giving you time to respond before threats spread further.
• Screenshot and application service verification: Every backup is tested automatically. You get visual proof and service-level validation that the backup is bootable and applications are functioning as expected — removing any uncertainty from your recovery process.

With Datto BCDR, MSPs and businesses gain complete confidence that their data is protected, their recovery points are valid and their operations can bounce back from disruptions without any delay.

Want to see how Datto BCDR delivers immutable, verified backups built for fast recovery? Explore the Datto BCDR solutions to learn more.

Looking to dive deeper into how immutability fits into a complete business continuity and disaster recovery strategy? Get your free copy of the Ultimate Guide to BCDR to discover why BCDR is a critical piece in the cybersecurity puzzle and to learn how to build a resilient BCDR strategy.