Data Immutability — Definition and Use Cases

Data immutability is the general term for preserving digital data in a form where it is not possible to change it or delete it once written. This may seem like a black and white definition, but because there are varying technology solutions, business requirements, and use cases, it contains a considerable amount of gray.

Immutability was originally based on media such as the magneto-optical disk, where the physics of the recording system enforced read-only behavior. This media could physically only be written a single time, earning it the moniker "write once, read many" or WORM. Tape systems such as LTO-WORM rely on firmware (embedded software) in the tape drive and special media to enforce immutability. Many other systems rely entirely on software to provide immutability, even though the underlying media on which the data is stored (HDDs and/or SSDs) is capable of being erased and rewritten. Hammerspace is such a software-based system.

Some define "data immutability" as the feature, and "WORM" as one of the technologies that may be used to achieve it. Most, however, just call it all WORM, which is much easier to say, type, and fit into a GUI or CLI. Because WORM is how the feature is referred to in the Hammerspace UI, the remainder of this document will use that term to refer to data immutability.

Hardware-based WORM technology is more secure than software-based approaches because there is no circumstance under which it can be bypassed or "turned off" by an administrator. But with security comes inconvenience. What if files only need to be immutable for a specific period of time? Or they need to be deleted when they are older than 7 years? Or dealing with unusual media like optical disks or tape is too disruptive or expensive? In these situations, software-based WORM is a better fit.

Specific business requirements may limit the acceptable options. Some industries are highly regulated and require certain types of data to be stored immutably using systems that meet specific regulatory requirements. Securities brokers and dealers, for example, must store records on a system that is certified to meet the requirements of SEC Rule 17a-4(f). This is only one example; an alphabet soup of similar regulations exists across many industries and global regions.

When WORM isn’t mandated by regulations, it is still a useful tool for safeguarding assets from modification or deletion. Ad agencies save final versions of video and print ads. Semiconductor companies archive finished chip designs. In general, any industry that produces digital products and needs to protect completed designs may want to use WORM technology to do so. WORM is also an excellent defense against threats like ransomware when it is used to protect static data assets or backup images.

Two categories of WORM technology exist to meet these different requirements, commonly referred to as "Compliance" WORM, and "Enterprise" WORM. Compliance WORM solutions are certified to comply with one or more industry regulations requiring immutability and are thus suitable for storing regulated data in those specific industries. All other solutions fall into the Enterprise WORM category. It is possible for a single product to have multiple modes, where it may be operated in Compliance mode, Enterprise mode, or both.