On Tue, 16 Apr 2013, David Brown wrote:
you are going to have terrible RMW performance for small writes. However, as
As I said, I don't have problem with lower performance. My workload is write once and few, read many. If the performance is approximately the approximately the same as a 10 drive RAID-6, but with double the storage, I'm fine.
I am not sure there is much real-world need of triple parity raid for normal arrays - even with better cpu scaling, it would still be a lot slower than two raid6 arrays LVM'ed together. I foresee it's main use as a temporary measure during array maintenance. For example, if you have a raid6 and you want to swap out the drives for bigger ones, then you could temporarily add an extra drive for a third parity using a non-symmetrical layout. Once this extra drive is synced, then you can step through the other drives doing a replace-and-resync, knowing that you still have the double parity safety. Then at the end of the process you drop the third parity again.
Well, I run RAID6+spare. I'd rather run a triple parity drive unless the write performance penalty is huge.
-- Mikael Abrahamsson email: swmike@xxxxxxxxx -- 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
