On Sun, August 23, 2009 3:48 am, Igor Podlesny wrote: > 2009/8/23 Drew <drew.kay@xxxxxxxxx>: >>>     "... It can also be used when creating a RAID1 or RAID10 if >>> you want >>> to avoid  the  initial  resync ..." >>> >>>     I'm wondering why namely those levels are chosen and not >>> RAID5/6 for e. g.? >>> >>>     I think it's also safe to use with RAID5/6, isn't it? >> >> RAID1/10 don't have parity calculations whereas RAID5/6 do. > > Well, and what does it change? I mean if we write some data to that > "assume clean" RAID5/6 the parity will be updated anyway. > Yes it will be updated. But if it is updated with a read-modify-write cycle then an old incorrect value will be updated to a new incorrect value, which doesn't help you much. The current RAID6 implementation never does read-modify-write for P/Q update so you could get away with --assume-clean there, but I don't promise that future implementations will never use r-m-w. RAID5 definitely does use R-M-W for single-block writes on arrays of 4 or more drives. NeilBrown -- 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
