Re: FYI: RAID5 unusably unstable through 2.6.14

[Erik Mouw]

On Tue, Jan 17, 2006 at 07:12:57PM -0500, Kyle Moffett wrote:
> The most reliable RAID-5 you can build is a 3-drive system.  For each  
> byte of data, you have a half-byte of parity, meaning that half the  
> data-space (not including the parity) can fail without data loss.   
> I'm ignoring the issue of rotating parity drive for simplicity, but  
> that only affects performance, not the algorithm.  If you want any  
> kind of _real_ reliability and speed, you should buy a couple good  
> hardware RAID-5 units and mirror them in software.

Actually, the most reliable RAID-5 is a 2 drive system, where you have
a full byte of reduncancy for each byte of data. Two drive RAID-5
systems are usually called RAID-1, but if you write out the formulas it
becomes clear that RAID-1 is just a special case of RAID-5.


Erik

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