Lock up data with fixed-content storage


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Protecting CAS data
Protecting data stored on a content-addressed storage (CAS) device presents an interesting dilemma for users because one of the primary purposes of a CAS product is to serve as a final resting place for data in an unchangeable format. Hewlett-Packard Co. deploys each of its SmartCell storage nodes in a mirrored configuration--each node keeps a mirror of its partner's data. In the event that one-half of the mirror fails, a free node in the grid is allocated as a replacement partner to mirror the data; the failed mirror can then be repaired and re-inserted in the grid.

EMC Corp. recommends replicating data to a second

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Centera at another site, but this is a costly alternative. To reduce the cost of a high-speed link between the two sites, the Centera Backup and Recovery Module (CBRM) allows existing backup software to connect to the Centera and back up its data to tape using the NDMP protocol. CAS products from Bycast Inc., IBM Corp. and Nexsan Technologies Ltd. allow you to copy each file or object to tape. However, this process re-introduces concerns about data integrity because someone needs to be responsible for moving the tape offsite and managing it in the long term.

Another consideration when evaluating each vendor's RAIN architecture implementations is the type of hardware to be used. Although each vendor uses off-the-shelf Intel server hardware to host its software, Archivas' ArC and Permabit's Permeon Compliance Store allow users to choose any vendor's brand of server, while CAS vendors such as EMC and HP require users to purchase server and storage hardware from them. HP only sells and certifies its ProLiant DL380 servers as nodes to support its StorageWorks RISS software.

Users with existing server hardware or server agreements may opt for Archivas' ArC or Permabit's Permeon Compliance Store because they run on any server vendor's hardware. For firms more concerned with deploying an end-to-end configuration sold and supported by a single vendor, choosing EMC or HP for the hardware and software in a preconfigured CAS product may be a better option.

The hashing algorithms a CAS product uses to create digital identifiers for each object is also important. Some hashing algorithms may be cracked or hacked over time; having the ability to upgrade the digital signature may therefore become more important. Caringo Inc.'s CAStor, a new CAS software product, lets users upgrade the hashing algorithm and digital signature as new ones become available.

Most RAIN architectures support only nodes with internal disk drives. Only Bycast's StorageGrid and Caringo's CAStor let users deploy nodes that support different types of external storage and manage the placement of data on these different tiers of storage based on policies set by users.

This was first published in June 2006

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