Raid 6 in use?

In article , Faeandar wrote:

Prior to this post I had never heard of raid 6 and have (still) no
idea what it's structure is. Going on Malcolm's allusion I assume
Double Disk Parity or Diagonal Parity or whatever is raid 6 nowadays?

There is a RAID6 implementation for Linux software RAID out there (and
I believe some folks are already using it in production). Perhaps
the details of it would clear this up a bit.

--
Joshua Baker-LePain
Department of Biomedical Engineering
Duke University

In article ,
Joshua Baker-LePain wrote:
In article , Faeandar wrote:

Prior to this post I had never heard of raid 6 and have (still) no
idea what it's structure is. Going on Malcolm's allusion I assume
Double Disk Parity or Diagonal Parity or whatever is raid 6 nowadays?

There is a RAID6 implementation for Linux software RAID out there (and

ITYM "RAID6"

HTH

--
Thor Lancelot Simon
But as he knew no bad language, he had called him all the names of common
objects that he could think of, and had screamed: "You lamp! You towel! You
plate!" and so on. --Sigmund Freud

Benno... wrote:

Nik Simpson wrote:

I think you'll find that RAID 6 is usually defined as a mechanism using
two different parity/ECC schemes such that a set can survive the loss
of any two disks.



I stand corrected, I realised that HP had defined RAID-6 this way, but
I din't realize that is a generally accepted definition.


I think HP/Compaq calls this Advanced Data Guard (ADG). Isn't the RAID-6
name copyrighted to someone?

You may be thinking of "RAID-7" from Storage Computer about 10 years
ago. It was a glorified RAID-4 box with vocal marketing.

RAID-6 is mentioned in the original Berkeley papers. They showed an NxM
matrix of disks with parity across and down. As other responders have
mentioned, there are ways to do N+2 directly.

One method (by Blaum at IBM, US patent 5271012 + others) is "even odd",
which uses diagonal parity for the second check disk. There is at least
one variant of this I've seen in a paper and at least one patent
application for a variant.

The Rabin paper mentioned in earlier responses discusses "information
dispersal", which can provide N data + M check disks. There is also a
paper "Tolerating Multiple Failures in RAID Architectures with Optimal
Storage and Uniform Declustering" by Guillermo Alvarez, Walter Burkhard,
and Flaviu Christian of UCSD (I got it online but don't have a URL).
The basic method is to define an N by N+M matrix where the first NxN
elements are an identity matrix and all N+M columns are linearly
independent. Encode the data by multiplying the data (in N chunks) by
the matrix. Recover data by multiplying the N returned chunks (data or
parity) by the inverse of the NxN matrix formed by using the columns for
the chunks recovered.

See also US patent 6557123 by Joseph Wiencko, assigned to Inostor. It
appears to be a form of the information dispersal method, but I've just
scanned the patent, not tried to read it in detail.

Thomas Wicklund