On 11/06/11 19:14, Joe Landman wrote:
A quick note of caution (and someone from Netapp, feel free to speak up). Netapp has a patent on triple parity raid (c.f. http://www.freepatentsonline.com/7640484.html). A quick look over this, suggests that the major innovation is the layout and computation which they simplified in a particular manner. That is, I don't think their patent covers triple parity RAID in general, but does cover their implementation, and the diagonal parity with anti-diagonal parity (effectively counter propagating or orthogonalized parity). I am not sure what this means from a coding sense, other than not to use their techniques without a license to do so. If Netapp wants to grant such a license, this would be good, but I suspect that it wouldn't be quite as simple as this. Just a note so that we don't encounter problems. I think its very possible to avoid their IP, as it would somewhat hard to claim ownership of the Galois Field math behind RAID calculations. They can (and do) claim a particular implementation and algorithm. [also not trying to open the patent on code wars here, just pointing out the current situation ]
I've read a little about diagonal parities - I can see some advantage in their simplicity, but I think that they are a poor choice for raid. Raid5+ already suffers from performance issues because you often have to read a whole stripe at a time just to change a few blocks - with diagonal parity, you'd have to read a whole 2-D set of stripes.
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