H. Peter Anvin wrote: > Peter Rabbitson wrote: >> Hi, >> >> I am experimenting with raid6 on 4 drives on 2.6.27.11. The problem I am >> having is that no matter what chunk size I use, the write benchmark >> always comes out at single drive speed, although I should be seeing >> double drive speed (read speed is at near 4x as expected). > > I have no idea why you "should" be seeing double drive speed. All > drives have to be written, so you'd logically see single drive speed. > Because with properly adjusted elevators and chunk sizes it is reasonable to expect N * S write speed from _any_ raid, where N is the number of different data bearing disks in a stripe, and S is the speed of a hard drive (assuming the drive speeds are equal). So for raid5 we have N = numdisks-1, for raid6 numdisks-2, for raid10 -n4 -pf3 we get 4-(3-1) and so on. I have personally verified the write behavior for raid10 and raid5, don't see why it should/would be different for raid6. In any case the witnessed problem was due to a hardware misconfiguration, which has not been resolved to this day. Thus thread is dead :) -- 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
