On Mon, Oct 03, 2011 at 09:07:44PM +1100, NeilBrown wrote: > The default for chunksize should be 512K I thought.. It is. > I once saw a mathematical formula, but it was a function of the number of > concurrent accesses and the average IO size - I think. > > Big is good for large streaming requests. Smaller is good for lots of random > IO. Only way to know for sure is to measure your workload on different sizes. > > You can change it once the array is build, but it is a very slow operation as > it has to move every block on every disk to somewhere else. > > mdadm -G /dev/md2 --chunk=32 FYI: For XFS I always get much better results using 32k chunk size, even for simple streaming reads/writes. I haven't really tracked down why. Also for any modern system I always have to massively increase the stripe cache size. -- 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
