Software-based WORM: How it works

Until recently, the term write-once, read-many (WORM) referred to characteristics of optical media, in particular the actual physical changes that occurred on the surface of an optical disk as a laser etched marks on it. But that distinction isn't as meaningful anymore, because storage vendors have sought to incorporate WORM characteristics into nonoptical media.

EMC Corp., for example, is providing software-based WORM functionality in its Centera system, which uses hard drives instead of optical disks.

The EMC system uses three main techniques: digital fingerprinting, retention protection and integrity checking. The system assigns a digital fingerprint or content address to each unique object. The fingerprint is calculated from a binary representation of the exact digital content of an object. Any change to that object will result in a completely new content address.

Each record stored in Centera is assigned a retention period that is embedded within the object's metadata. That record cannot be deleted until its retention period has expired.

Finally, integrity checking continuously monitors the authenticity of each content address to ensure that authenticity has not been compromised throughout the record's life cycle.