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RAID6 is intended to provide fault tolerance in the event 2 disks fail.

What is the minimum number of disks required to implement RAID6?


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migrated from stackoverflow.com Mar 13 '10 at 12:22

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3 Answers

Did you do any investigation yourself?


4 disks = 2 for data, 2 for parity.

I suppose you could get away with 3 disks, but why have 2 parity for 1 data?

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I don't think any controller is going to let you do a RAID 6 with only 3 disks. It will force you to do a RAID 5. If it does let you do a RAID 6 with three disks, I would stop using that RAID card right away since it can't be reliable at all. –  Urda Mar 13 '10 at 17:38
RAID6 over three disks is in fact equivalent to RAID1... –  b0fh Mar 13 '10 at 19:07
@b0fh, @Urda: personally, I've never tried RAID 6 and have never heard of anyone using it until now. With 4 disks, why not RAID 10 for example? –  gbn Mar 14 '10 at 9:04
With raid10, if you randomly lose 2 disks, there is a 1/3 chance of them being the same stripe, and you lose the whole array. Raid6 will guard you against any combination of 2 drives failing (but is computationally more expensive, and has lower parallelism as well) –  b0fh Mar 14 '10 at 12:43
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It makes a lot of sense to go for a 3 disk raid 6.

Its the most efficient config that can handle 2 failures. I can assure you that its a very nervous time when you loose one disk on a raid 1 or 5 system, especially when you know that the disks were bought at the same time which increases risk dramatically. With Raid 6 you can still be quite laid back about it.

After a disk fail you pull the wrong disk out, whoops, with raid 6 its stressful but not fatal.

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Since you need a double level of parity it should be 4 disks. You split the data on 2 disks while you calculate different parities on the other ones..

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