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# How to calculate parity for Raid 6 if 2 disks go down?

Tags:
• NAS / RAID
• Storage
Last response: in Storage
October 14, 2010 1:47:45 PM

Hi,

Let us suppose I have 6 disks A,B,C,D,E,F having data bits 1 1 0 0 1 0 in respective disks. now please let me know how to get the data if 2 disks suppose E and F go down. Please reply ASAP..

Thanks,
Asif Masood

More about : calculate parity raid disks

a c 464 G Storage
October 14, 2010 4:38:31 PM

YOU don't have to do any of this. The RAID controller does all the work.

However, if you want to understand how that is done, read this Wiki article:

http://en.wikipedia.org/wiki/Standard_RAID_levels

In RAID5, the "parity" data is actually an XOR function of the four sets of data in the stripes. In RAID6, this is only the first operation. The second is much more complex involving both an XOR function and a bit shift function. BOTH generate "parity" data that are stored in the stripes of the array. I don't have anywhere near the math knowledge to understand it, but maybe you can grasp more of it from the link and other references.
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October 16, 2010 5:35:09 AM

Thanks for the link.. Do you have any other link in which its explained more easy way. This is really confusing one.
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a c 464 G Storage
October 21, 2010 3:51:18 AM

I agree it's confusing. I don't understand it, and that is why I never tried to do it. the point is that the RAID controller is supposed to do all the work for you. You are only supposed to read the RAID manual for your system and follow the instructions for how to monitor for problems and how to use the software utilities provided with it to restore a degraded array.
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November 15, 2010 4:01:52 PM

Thanks.
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