What is CAS?

Storage managers are quickly realizing that not all corporate data is alike and different data must be handled in ways that benefit the business. While storage arrays are often employed for fluid or transaction-based corporate data, they generally fall short with long-term or archival storage tasks. Content-addressed storage (CAS) is one emerging disk-based storage technology that promises to improve the storage of long-term fixed content by lowering storage costs, ensuring file authenticity and reducing storage requirements.

CAS systems are designed to store fixed data that rarely, if ever, changes and is only called for infrequently. For example, a corporate Oracle database must be continuously accessible from high-performance Fibre Channel storage. Yet, a vast amount of business data, like patient medical images or legal documents, is only needed occasionally. Consequently, CAS platforms can offer lower storage costs using inexpensive high-density SATA or SAS hard disks -- similar to other second-tier storage solutions.

"CAS is really used as a lower cost tier of storage typically used as an online digital archive," says Tony Asaro, senior analyst at the Enterprise Strategy Group. "Customers put files, e-mail and even database data on CAS as a large repository."

Increasing regulatory demands and litigation are also prompting corporations to examine their data integrity. Today, it's not enough to simply store data. Storage managers must implement strategies to ensure that files can be located promptly by auditors and legal staff on demand, and prove, often in a courtroom, that e-mails, documents and other types of data have not been changed or tampered with. CAS ensures data integrity, because in CAS systems data exists as annotated "objects" that cannot be duplicated or modified.

Still, CAS has its downsides. CAS platforms are yet another addition to the storage infrastructure that must be managed and maintained. CAS is not an appropriate solution for high-performance transactional storage tasks -- it's strictly a secondary storage system. Software is also a vital component of CAS operation and management, so it's important to consider the overall quality of hardware, software and network integration prior to any CAS acquisition. The following article outlines the essential ideas of CAS, offers vendor and user insights into existing products, and examines potential future directions of the technology.

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