2017-03-21 11:54 GMT+01:00 Adam Goryachev <mailinglists@xxxxxxxxxxxxxxxxxxxxxx>: > I can't say I'm an expert in this, but in actual fact, I disagree with both > your arguments against RAID6... > You say recovery on a RAID10 is a simple linear read from one drive (the > surviving member of the RAID1 portion) and a linear write on the other (the > replaced drive). You also declare that there is no random IO with normal > work load + recovery. I think you have forgotten that the "normal workload" > is probably random IO, but certainly once combined with the recovery IO then > it will be random IO. > > In addition, you claim that a drive larger than 2TB is almost certainly > going to suffer from a URE during recovery, yet this is exactly the > situation you will be in when trying to recover a RAID10 with member devices > 2TB or larger. A single URE on the surviving portion of the RAID1 will cause > you to lose the entire RAID10 array. On the other hand, 3 URE's on the three > remaining members of the RAID6 will not cause more than a hiccup (as long as > no more than one URE on the same stripe, which I would argue is ... > exceptionally unlikely). > > In addition, with a 4 disk RAID6 you have a 100% chance of surviving a 2 > drive failure without data loss, yet with 4 disk RAID10 you have a 50% > chance of surviving a 2 drive failure. > > Sure, there are other things to consider (performance, cost, etc) but on a > reliability point, RAID6 seems to be the far better option. Totally agree -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
