Discussion Forums > Technology
RAID Boxes
Talapus:
I understand how parity works on RAID 2-5. But can anyone explain how the double parity in RAID 6 works? I've done some reading on R-S code, and while I can understand most of the math, I can't seem to put the pieces together. ???
halfelite:
It works the same as raid 5 except the parity is on two drives. its like the parity chunks is raid 1 and mirrors to another drive. So you can technically lose 3 drives before you lose data.
Talapus:
--- Quote from: halfelite on August 04, 2009, 05:15:39 PM ---It works the same as raid 5 except the parity is on two drives. its like the parity chunks is raid 1 and mirrors to another drive. So you can technically lose 3 drives before you lose data.
--- End quote ---
No. Normal parity (including mirrored parity) cannot compensate for the loss of two data blocks for a given stripe. And since RAID 6 rotates parity, that would mean the the loss of ANY two drives would compromise the data integrity.
If you had mirrored parity and dedicated parity drives, you could loose both parity drives, or one parity drive and one data drive (but not two data drives).
Arveene:
RAID 6 will remain intact with the loss of any two drives. One more drive loss before it's rebuilt will wipe out the array.
The wikipedia page has a little bit on the math and links this as it's source. It might be worth a read.
halfelite:
--- Quote from: Talapus on August 04, 2009, 05:33:45 PM ---
--- Quote from: halfelite on August 04, 2009, 05:15:39 PM ---It works the same as raid 5 except the parity is on two drives. its like the parity chunks is raid 1 and mirrors to another drive. So you can technically lose 3 drives before you lose data.
--- End quote ---
No. Normal parity (including mirrored parity) cannot compensate for the loss of two data blocks for a given stripe. And since RAID 6 rotates parity, that would mean the the loss of ANY two drives would compromise the data integrity.
If you had mirrored parity and dedicated parity drives, you could loose both parity drives, or one parity drive and one data drive (but not two data drives).
--- End quote ---
That is what I ment. 2 drives down and you still have a functioning system to rebuild with. One more loss and you are out of luck.
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