The concept of parity-based RAID (levels 3, 5 and 6) is now pretty old in technological terms, and the technology's limitations will become pretty clear in the not-too-distant future — and are probably obvious to some users already. In my opinion, RAID-6 is a reliability Band Aid for RAID-5, and going from one parity drive to two is simply delaying the inevitable.
The bottom line is this: Disk density has increased far more than performance and hard error rates haven't changed much, creating much greater RAID rebuild times and a much higher risk of data loss. In short, it's a scenario that will eventually require a solution, if not a whole new way of storing and protecting data.
We'll start with a short history of RAID, or at least the last 15 years of it, and then discuss the problems in greater detail and offer some possible solutions...
 
 
 
 
 
Linux Kernel Development How Fast it is Going, Who is Doing It, What They are Doing, and Who is Sponsoring It: An August 2009 Update
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