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RAID DDF is designed to allow users to swap their vendor's RAID device for another to do what's called an inplace migration. "If a customer has a RAID set on a server that's direct-attached, and then wants to move that to an internal enclosure, you can migrate the RAID set," explains Larry Lamers, director of technology and standards at Adaptec Inc. and secretary of the DDF TWG. The other key benefit is if users run into a failure with a specific RAID controller, they can replace it with a different vendor's controller, in place of the original.
Lamers says that the TWG is "pretty much in agreement" over what the standard should include. "This one was pretty straightforward." Interoperability testing should take place the first half of next year, with products on tap for late 2005, he says. The group is currently working on profiles that define interoperability points.
The standard currently includes two basic elements. One is a data structure, to define which level of RAID has been implemented. This lets every disk know which other disks are part of the RAID configuration. The second piece is the actual layout--stripe size, stripe depth, etc. Today the metadata that describes how each vendor represents its RAID device is supplier-specific, and the goal is to allow RAID disks to recognize each other.
Although the DDF's list of supporters and participants isn't public yet, Lamers says, "I can't think of any RAID vendor with any significant market share that's not involved in this. Some came in late, but everybody pretty much joined the parade."
So far there have been two prototype implementations of DDF, says Ramamurthy Krithivas, an architect with Intel Corp.'s storage components division and a member of the TWG. He says he'd like to see the next version of the DDF incorporate a basic reporting mechanism for RAID 6 that wasn't included in the first version of DDF "because of all the complexities" involved. "I'm talking about the configuration information, not the layout, because the layout is where vendors add value."
This was first published in October 2004