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Immutable storage: What it is, why it's used and how it works

By Julia Borgini

Immutable storage refers to data that cannot be modified or deleted once written. This characteristic ensures the data remains static and pristine, protecting it from unauthorized changes, even by system administrators.

In a digital world that faces increasing cyberthreats, immutable storage offers a strong defense mechanism. There's a lot more to it, though, with many uses, features, benefits, challenges and types for admins to consider.

Why is immutable storage important?

Organizations use immutable storage to maintain data integrity and comply with regulatory requirements, making it essential for data protection, preservation and security. It safeguards against cyberthreats like ransomware and accidental deletions, ensuring reliable access to unaltered data for auditing and regulatory compliance purposes.

Immutable storage is particularly crucial in industries such as finance and healthcare, which have strict data retention and protection mandates.

How immutable storage works

Immutable storage operates on a write once, read many (WORM) principle. Data becomes unalterable after users save it once. Users can access the data but can't modify it without appropriate permissions. Other key features include the following:

• Access controls ensure only authorized users, processes or systems can write to the storage, while others can only read it.
• Retention policies specify how long data must remain unchanged before it can be deleted. For example, Microsoft Azure allows retention policies from one to 146,000 days (400 years) for its Blob Storage.
• Audit logging records all interactions with the stored data.
• Hardware and software protections safeguard against physical and digital threats with tamper seals, secure hardware modules, distributed consensus algorithms and data hashing.
• Decentralization prevents single points of failure or manipulation.

Key benefits of immutable storage

Immutable storage offers many advantages to organizations, in addition to legal and regulatory ones.

Data security

Businesses in highly regulated industries, such as finance, healthcare and banking, enjoy the peace of mind immutable storage gives them. They know it protects their data from tampering by both external and internal sources, providing ransomware protection, for example.

Data integrity

Immutable storage guarantees the authenticity and trustworthiness of data, especially if organizations use it for audits and decision-making. Locking the data into a read-only state shields sensitive information from threats, human error and tech failures. It's easy to demonstrate its accuracy and freedom from alterations.

Drawbacks of immutable storage

The benefits generally outweigh the drawbacks. Immutable storage can't be deleted before its retention policy expiration date, but it can be costly and challenging to store. This is even more relevant for organizations that retain all immutable data permanently; the costs to store it all may be astronomical.

Cloud-based immutable storage can solve many of these challenges as users can expand capacity at lower cost. Many organizations opt for on-premises storage to reduce those costs even further.

All immutable data is susceptible to physical damage at the storage site, however. Organizations may want to consider a combination of on-premises and cloud-based immutable storage to take advantage of the duplication, replication and decentralization offered by the multiple locations.

Types of immutable storage

Immutable storage has two main types: on-premises and cloud-based.

On-site hardware stores immutable data in various platforms, such as WORM tapes; HDDs; SSDs; file system support features, like the Linux chattr command that enables immutable metadata protections; or specialized software that creates immutable storage environments through hashing and digital signatures.

Air-gapped storage is a type of on-premises storage that's only considered immutable when combined with other protections to prevent data from alteration or deletion. The device could be a physical hard drive, server or a logical air gap enabled by software on an air-gapped hard disk partition.

Cloud-based data storage services or systems accessed through the internet offer data immutability as a core feature. For example, Amazon S3, IBM Cloud, Oracle Cloud Infrastructure and Google Cloud offer unique object lock versions. Microsoft Azure offers immutable Blob Storage.

Immutable storage vs. immutable backup

While often confused, immutable storage and immutable backup are different.

Admins can use immutable storage to create an immutable backup for critical data needed for recovery. Immutable storage is for more than just backups, though. Here is how they differ:

• Immutable backup is a secure data copy that can't be altered or deleted. It's an unchanged copy of valuable data that enables access but cannot be overwritten.
• Immutable storage is a type of stored data that users cannot modify, delete or overwrite once they save it to the location or device.

Who uses immutable storage?

Various sectors rely on immutable storage for maintaining secure and unaltered copies of data, including the following:

• Law enforcement. Preserves digital evidence for legal proceedings, while ensuring compliance with custody standards, like the ISO chain of custody standard.
• Finance. Protects financial records from tampering, adhering to different regulations around the world, such as the Sarbanes-Oxley Act, the Payment Card Industry Data Security Standard, System and Organization Controls standards, and GDPR.
• Healthcare. Safeguards medical records and patient information against unauthorized access, complying with privacy laws, such as HIPAA.
• Government. Ensures the accuracy of public records for transparency for public scrutiny, supporting accountability for government activities.
• Education. Protects student information and academic records, while complying with privacy regulations, such as the Family Educational Rights and Privacy Act in the U.S.
• Tech and business. Fortifies data and production logs, adds another layer to cybersecurity efforts and helps organizations comply with data laws, such as GDPR.

Julia Borgini is a freelance technical copywriter, content marketer, content strategist and geek. She writes about B2B tech, SaaS, DevOps, the cloud and other tech topics.