What is content-addressable storage (CAS), and how does it work?

CAS is a way of storing information that can be retrieved based on its content, instead of its storage location. It's typically used for long-term storage and retrieval of fixed content, like documents stored with compliance for government regulations, or medical records like x-rays and MRIs. In other words, when you think about storage, everything has an address. For conventional file systems, it's a name and a location in a hierarchy of directories.

A CAS system uses the content itself as an address through a unique identifier, typically using a hashing algorithm performed against the content. That makes the content address unique. No two pieces of content have the same address unless the content is exactly the same.

Using content-addressing models provides three main benefits:

  1. The need for applications to understand the physical location of information is eliminated.
  2. A content address acts a digital fingerprint, which can be used for irrefutable authenticity during a legal or regulatory investigation.
  3. Digital fingerprints are used to identify and eliminate duplicate records, such as emails with attachments, which ultimately reduce archive capacity requirements.

Check out the entire CAS FAQ.

This was first published in June 2008

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