The 2006 Linux Filesystems Workshop (Part II) [LWN.net]

The 2006 Linux Filesystems Workshop (Part II)

Posted Jul 6, 2006 23:18 UTC (Thu) by valhenson (subscriber, #38407)
In reply to: The 2006 Linux Filesystems Workshop (Part II) by sveinrn
Parent article: The 2006 Linux Filesystems Workshop (Part II)

You might find NetApp's latest and greatest RAID stuff interesting:

"Row-Diagonal Parity for Double Disk Failure Correction"

Peter Corbett, Bob English, Atul Goel, Tomislav Grcanac, Steven Kleiman, James Leong, and Sunitha Sankar, Network Appliance, Inc.

http://www.usenix.org/events/fast04/tech/corbett.html

Awarded best paper at FAST '04... trying to remember if I've read it myself though, since I saw the talk.

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The 2006 Linux Filesystems Workshop (Part II)

Posted Jul 7, 2006 9:10 UTC (Fri) by sveinrn (subscriber, #2827) [Link]

I have looked at it. But as far as I can see, this scheme does not protect proberly against '"high-flying writes" and "over-powered seeks", "phantom writes" and "misdirected reads and writes."'

The parity schemes used in RAID are good for recreating data that is known to be missing. Error correcting codes (including the Hamming code) are good for correcting data that is readable but corrupt. So my first thought was that with RAID6 on top of the Hamming code we would be protected from 2 failed disks in combination with 1 corrupt disk. But that is clearly wrong. So a better idea could be one of the more modern codes, for example the Reed-Solomon code. That also removes the need for RAID6 parity on top. (The Reed-Solomon code is also especially effective when one knows where the error is, i.e. a missing disk.)