Special Section: SNW, Fall 2004 - Highlights From The SNW Floor:

THE SNIA APPROVES NEW COMMON RAID DISK DATA FORMAT ARCHITECTURE

The Storage Networking Industry Association (SNIA) announced the approval of the Common Redundant Array of Independent Disks (RAID) Disk Data Format (DDF) architecture. Designed by the DDF Technical Working Group (TWG), the Common RAID DDF architecture provides a standard method for storing RAID configuration information on physical disks, thus enabling interoperability between different RAID suppliers.

"We are very excited about this new architecture from the DDF TWG," said Sheila Childs, chair emeritus of the SNIA Board of Directors. "This development holds great promise for end users faced with the common task of migrating data from one RAID solution to another. By standardizing configuration information in a common format, the DDF architecture will take a big step toward plug-and-play RAID interoperability, ultimately providing increased choice and flexibility for end users."

The DDF architecture defines a standard data structure describing how data is formatted across the disks in a RAID group and ranges in scope from RAID On the Mother Board (ROMB) to PCI-based RAID controllers for internal and direct attached storage. The DDF stores RAID configuration information on physical disks by different vendor implementations in a common format so the user date on the disks is accessible independent of the RAID controller being used.

Bill Dawkins, chair of the DDF TWG said: "Today, users are faced with the fact that RAID vendors use a different configuration data format, and many times the formats vary within the same vendors' product families. Ensuring users have the correct RAID configuration when they need to replace a RAID controller or transfer data from one to another has been a daunting task. The Common RAID DDF removes these user pain points by reducing the risk of losing that data due to RAID incompatibility."

The DDF architecture resides on every disk behind a RAID controller. When disks containing a RAID group are transferred to a new controller, the configuration information is transferred with the group. Standardization allows the new controller to determine the arrangement of the user data on the disks. Even if a RAID group containing a unique format is moved to a different RAID solution that does not support the format, the DDF will allow detection of the non-compatible configuration. This mitigates the potential for data loss because the new RAID system will not overwrite the data without administrator confirmation. This is a tremendous value to the end user as it prevents accidental loss of data during migration or certain disaster recovery scenarios.

The DDF structure describes features such as the controller data, physical drive data (online state) virtual drive data (initialization state), sparing assignments, bad block management, vendor specific logs and virtual drive configurations such as RAID levels, and participating drives stripe size and cache policies.

The DDF has been submitted to the InterNational Committee for Information Technology Standards to begin the standardization process.