Writeonce

Writeonce refers to data that is written one time and then not modified or overwritten. In information technology, write-once semantics are implemented to preserve integrity, support auditing, and comply with regulatory retention requirements. The term is commonly encountered as Write Once, Read Many (WORM).

Implementation is achieved through physical media designed to restrict rewriting, such as write-once read-many storage. Optical media like CD-R and DVD-R are classic examples; certain magnetic tapes and magneto-optical media offer WORM capabilities. Modern hardware may provide one-time programmable (OTP) flash memory or secure elements that allow a value to be written only once. In software and cloud environments, write-once can be realized via immutability features that lock objects or blocks for a retention period, often configurable by policy.

Applications include archival storage for legal and regulatory compliance, long-term backups, and tamper-evident logging. In cloud storage, features such as object locks or retention policies enable customers to enforce immutability for a set duration, protecting against accidental or malicious deletion.

Limitations: true immutability depends on the lack of external revocation; physical or administrative controls may fail; once content is written and the device is accessible, it could be copied or extracted; costs and capacity considerations; a retention window may be specified but cannot be indefinite without policy. Best practices combine encryption, access controls, and audit trails.

See also: WORM, immutable storage, append-only log.