Take the 2-minute tour ×
Server Fault is a question and answer site for professional system and network administrators. It's 100% free, no registration required.

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

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

thanks

share|improve this question

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

This question came from our site for professional and enthusiast programmers.

add comment

3 Answers

Did you do any investigation yourself?

http://en.wikipedia.org/wiki/RAID#RAID_6

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?

share|improve this answer
    
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
1  
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
2  
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
add comment

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.

share|improve this answer
add comment

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..

share|improve this answer
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.