Friday, August 26, 2011

Difference between RAID5 and RAID 5+0/RAID6 and RAID60

Let's consider what is common between RAIDn and RAIDn+0 and how do they differ?
  • given arrays are the same with regard to fault tolerance;
  • RAID 5 and RAID 50 can withstand only one member disk failure;
  • RAID 6 and RAID 60 can survive two disks failure supposing we talk about a 100% probability.
RAIDn+0 arrays have more chances to survive more than one (in RAID50) or two (in RAID60) member disks failure, although not a 100% probability. You can estimate survival probability for various RAID layouts at

  • During the rebuild, RAIDn+0 delivers greater performance as compared to RAIDn which is good.
  • RAIDn+0 overhead to provide fault tolerance is more than for RAIDn arrays. RAIDn+0 overhead is one disk per each RAIDn disk group.
Let's make a conclusion - RAID n+0 should be used in case of a large storage while RAIDn - in small (I mean number of disks) arrays.

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