Why is it generally considered that RAID 5 systems are not suitable for larger disk sizes? Is the same true for RAID 6?


RAID5 is unsuitable full stop

A good explanation (from 5 years ago) is here:


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  • I understand the risk of multiple drives failing, before the rebuild is complete, increases. But RAID6 can deal with 2 disk failures. Is RAID6 suitable for large disk sizes? – Anthony May 9 '15 at 13:43
  • @Anthony sure, if you don't care much about performance. – jordanm May 9 '15 at 14:02
  • You only pay a performance penalty with RAID-5/6 if you don't know how to build a RAID array and/or don't know how to align IO operations. If you go and build a 14+2 RAID-6 arrays, sure you'll have performance problems. But, for example, if you build 8+2 RAID-6 arrays and know to select proper segment sizes and partition alignments so that the file system you build on top of the arrays(s) writes full RAID stripes that are aligned, you won't see any performance issues. 14+2 arrays are like buying a Ferrari, putting it in 6th gear while stopped, popping the clutch, and then saying it's slow. – Andrew Henle May 9 '15 at 17:10
  • @Anthony Even with 2 parity drives, you have to remember you have disks that are all the same age. One has failed and all of a sudden you massively increase the load on the others to rebuild. This increases the chance of another one failing, or even 2 (which would be a bad thing). – chriscowley May 11 '15 at 7:11

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