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Could anyone tell me which RAID would be the best between 10 and 01, and why?

Thanks for your help.

EDIT: I didt't want to know what's the best RAID ever... Otherwise I'd ask: "Why is NetApp RAID-DP so much better than EMC's RAID-6??". My question was purely to know what's the difference between the RAID 10 and 0+1, cause it wasn't clear for me at the time. It has been greatly answered, thanks for the people who understood the sense of the question. Next time I will detail it a bit more, I take the whole culpability on that one!

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5 Answers 5

up vote 7 down vote accepted

It's 10 (1+0), rather than 0+1 - because mirrored stripes are more likely to handle multiple disk failures than striped mirrors.

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No. 1+0 and 0+1 have exactly the same disc failure setup in a good raid controller. I suggest you take a piece of paperand work out sector layouts. A good controller can survive exactly the same amount of disc failures. –  TomTom Oct 1 '10 at 11:38
    
@TomTom; while some controllers can tolerate failures the same in 10 as 0+1, many do not. So without knowing, it's safest to recommend 10. –  Chris S Oct 1 '10 at 12:30
    
@TomTom: can you explain how those controllers manage to tolerate a second failure in a two element RAID 1? –  Javier Oct 1 '10 at 16:11
    
@TomTom - having seen your own answer I can see why'd you'd comment on mine, you've not thought about it or had any experience of the difference - you do have the option of not answering or commenting on a question you know? –  Chopper3 Oct 2 '10 at 22:14
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To give more detail: with four drives there are six combinations of two-drive failures (1 & 2, 1 & 3, 1 & 4, 2 & 3, 2 & 4, and 3 & 4). RAID10 will survive 4 of these combinations (where the two failed drives are on different legs) and RAID0+1 will survive the other two (where both failed drives are on the same leg). I'm not sure when/how 0+1 would be better (perhaps there is a performance difference in some special circumstances) but for redundancy, other things being equal, 10 is preferable. –  David Spillett Oct 4 '10 at 16:31

Sorry, but... "best" for which purpose?

IMHO the main difference is that usually raid 1+0 has better redundancy that 0+1. In case of a disk failure, in raid 1+0 usually the redundancy is lost only for one stripe, while in 0+1 the entire side of the mirror is lost.

I wrote "usually" several times because a lot depends on the specific RAID implementation.

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Since there's no gain in 0+1, but a potential gain in 1+0 (depending on the controller), why would you ever recommend 0+1?? –  Chris S Oct 1 '10 at 12:32
    
In some software implementation it is possible to have different topology in the two sides of the mirror: for example one can be striped, the other concatenated. This can give you more flexibility, for example if you have to temporarily mirror something. –  marcoc Oct 1 '10 at 12:47

the point is what happens when a second failure strikes before you fix the first one:

  • striped mirrors: 1/(n-1) chances it will take your data with it.

  • mirrored stripes: (n/2)/(n-1) chances of the same disaster.

which one would you bet your job on?

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While I agree that RAID 0+1 doesn't make sense, if you're designing a solution that needs to survive two failures, neither solution is necessarily going to do so. If you bet your job on RAID 10, it is a better bet, but you're still gambling. –  duffbeer703 Oct 1 '10 at 12:43
    
obviously, the real safeguard is the backup, RAID buys you availability, not safety. for that, there's no 'absolutely never', only statistics and probabilities. –  Javier Oct 1 '10 at 16:08

Everyone else's answers are fine, but if your RAID provide supports RAID 6 (sometimes called ADG), use that. RAID10 (or 1+0 or 0+1 can lose up to two disks and still be useful... But if two of the wrong disks die, your entire array is toast.

RAID6 is like RAID5 but with an additional Parity disk can lose ANY two disks and still be functional. I'd go with that.

OBLIGATORY MESSAGE: RAID IS NOT BACKUP! You still need to do them.

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RAID6 is much slower on cheaper controllers; and still slower even on the best controllers than RAID10. –  Chris S Oct 1 '10 at 12:33
    
RAID-5 and RAID-6 are parity schemes that have significant performance disadvantages in many applications. Write speeds are significantly slower with RAID-5, and in the event of failure, performance of the volume is compromised. So while you're protected against data loss, you may have a service impact. With RAID 10 or RAID 1, a disk failure has no service impact. –  duffbeer703 Oct 1 '10 at 12:40
    
I've never benchmarked them to compare, and I've personally never had complaints about any performance hit. For me and my environments, the safety net that comes from not worrying when the next shoe will drop is worth it. (Even though I have good backups.) Classic case of 'Speed vs. Robustness.' –  gWaldo Oct 1 '10 at 12:41
    
In any case, the user didn't post his criteria for "best". Also, we know nothing about his server, environment, load-balancing/clustering capabilities, or application. –  gWaldo Oct 1 '10 at 12:51
    
I guess NetApp's RAID DP would be one of the best solutions for security, fast access and backup, protecting from data loss. –  waszkiewicz Oct 4 '10 at 10:24

which RAID would be the best between 10 and 01, and why?

Well, between 10 and 01 you have.... 5.5, so look for a Raid 5.5. Sorry, there is no other answer that makes sense - only my sarcastig one.

Otherwise, the real answer is "it depends" on all levels. Raid 10 and 01 make no or a lot of difference depending how it is implemented (it must not make any difference, technically). Whether you raid first then stripe or stripe first then raid makes technically NO difference.

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4  
-1. There is a difference. RAID0 over RAID1 (RAID1+0 or RAID10) can survive four of the six possible two-drive failure cases in a four drive setup. RAID1 over RAID0 (RAID0+1) can survive the other two. 0+1 may be preferable where controller failure or loss of communication with the controller is more likely then two drives failing if the inner RAID0 arrays are on separate controllers, but otherwise RAID10 has a significant redundancy advantage. –  David Spillett Oct 4 '10 at 16:41

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