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Content-addressed storage safeguards retention data and prevents its alteration.
For most companies, fixed-content storage requirements are simple: Store the data securely, do it cheaply and provide fast access. With more data subject to external and internal audits, content-addressed storage (CAS) products are becoming the preferred storage medium for the long-term protection of fixed content.
CAS products come in four different architectures:
- The redundant array of independent nodes (RAIN) architecture is the predominant way vendors offer CAS hardware. Inexpensive servers or nodes with high-capacity disk drives are clustered together; software locks the data stored on each node. As growth occurs, more nodes are added to the RAIN cluster.
- Network Appliance (NetApp) Inc. presents a network file system over an Ethernet connection on the front end while using WORM technology to lock the data down and data deduplication to optimize its capacity. The system accommodates growth by adding more disk capacity to NAS head configurations or allowing upgrades to higher capacity NAS filers. There's no way to move data from the NetApp disk to tape or optical media.
- The hierarchical storage management (HSM) architecture offered by IBM Corp. allows applications to archive and retrieve data from the CAS system using APIs provided by the CAS software. IBM requires users to deploy its Tivoli Storage Manager (TSM) 5.3 for Data Retention software, which comes with its TotalStorage DR550. IBM's CAS product differs from the other CAS architectures because it doesn't use data deduplication or single-instance storage (SIS) by default, although users can deploy these technologies and use TSM to manage the data.
- Nexsan Technologies Ltd. offers a networked storage array architecture that includes CAS software as part of the array to manage data retention and ways to move data between disk, tape and optical.
There are trade-offs with each of these designs. Each one requires some type of software to classify and then move the data to and from the CAS device. Products using RAIN architectures--including Archivas Inc.'s Archiving Cluster (ArC), EMC Corp.'s Centera, Hewlett-Packard (HP) Co.'s StorageWorks Reference Information Storage System (RISS) and Permabit Inc.'s Permeon Compliance Store--store files as objects. This introduces a new format for storing files whose long-term management costs and liabilities aren't yet well understood. File-system approaches don't support SIS and require third-party products to manage file meta data. HSM architectures are based on a model that may not respond well with large data stores, while the network storage array approach has limitations on total disk capacity and the disk it will support.
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