On 7/29/25 00:23, Martin K. Petersen wrote:

quoted

b) io_opt, size to ???
 4) For raid0/raid10/rai5, this value is set to mininal IO size to get
    best performance.

For software RAID I am not sure how much this really matters in a modern
context. It certainly did 25 years ago when we benchmarked things for
XFS. Full stripe writes were a big improvement with both software and
hardware RAID. But how much this matters today, I am not sure.

FWIW, I just posted a patch that aligns writes to stripe boundaries
using io_opt:

https://lore.kernel.org/all/55deda1d-967d-4d68-a9ba-4d5139374a37@cybernetics.com/ (local)

I get about a 2.3% performance improvement with md-raid6, but I have an
out-of-tree RAID driver that gets more like 4x improvement.

If io_opt means different things to different code, might we consider
adding another field to the queue limits to give explicit stripe parameters?

Tony Battersby
Cybernetics