On Mon, 4 Sep 2017, Andreas Klauer wrote:
Genuine simultaneous drive failures are *very* rare.
No, the "drive failed and I now have URE on another drive" is not "*very rare*". Yes, it can be somewhat mitigated by frequent scrubbing.
That's why I run RAID6 and not RAID5. I have been hit by the above problem several times when running RAID5. I haven't yet had a data loss event (that I know of) because of this since I moved to RAID6.
I think "RAID6 with triple parity" would make sense for some deployment scenarios. It's not uncommon for people to have several RAID6 arrays and then have a hot spare in the chassis. This hot spare could instead actually do work by being triple redundancy in one array, instead of sitting there powered on but doing nothing.
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