Re: FYI: RAID5 unusably unstable through 2.6.14

[Phillip Susi]

Michael Loftis wrote:

> What about I said was inaccurate?  I never said that it increases 
> exponentially or anything like that, just that it does increase, which 
> you've proven.  I was speaking in the case of a RAID-5 set, where the 
> minimum is 3 drives, so every additional drive increases the chance of 
> a double fault condition.  Now if we're including mirrors and 
> stripes/etc, then that means we do have to look at the 2 spindle case, 
> but the third spindle and beyond keeps increasing.  If you've a 1% 
> failure rate, and you have 100+ drives, chances are pretty good you're 
> going to see a failure. Yes it's a LOT more complicated than that.

I understood you to be saying that a raid-5 was less reliable than a 
single disk, which it is not.  Maybe I did not read correctly.  Yes, a 3 
+ n disk raid-5 has a higher chance of failure than a 3 disk raid-5, but 
only slightly so, and in any case, a 3 disk raid-5 is FAR more reliable 
than a single drive, and only slightly less reliable than a two disk 
raid-1 ( though you get 3x the space for only 50% higher cost, so 6x 
cheaper cost per byte of storage ). 




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