On Tuesday March 6, rabbit@xxxxxxxxx wrote: > Neil Brown wrote: > > When we write to a raid1, the data is DMAed from memory out to each > > device independently, so if the memory changes between the two (or > > more) DMA operations, you will get inconsistency between the devices. > > Does this apply to raid 10 devices too? And in case of LVM if swap is on > top of a LV which is a part of a VG which has a single PV as the raid > array - will this happen as well? Or will the LVM layer take the data > once and distribute exact copies of it to the PVs (in this case just the > raid) effectively giving the raid array invariable data? Yes, it applies to raid10 too. I don't know the details of the inner workings of LVM, but I doubt it will make a difference. Copying the data in memory is just too costly to do if it can be avoided. With LVM and raid1/10 it can be avoided with no significant cost. With raid4/5/6, not copying into the cache can cause data corruption. So we always copy. 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
