Sequential read from NVMe/XFS twice slower on Fedora 42 than on Rocky 9.5

[Dave Chinner]

On Tue, May 06, 2025 at 02:03:37PM +0300, Anton Gavriliuk wrote:
> > So is this MD chunk size related? i.e. what is the chunk size
> > the MD device? Is it smaller than the IO size (256kB) or larger?
> > Does the regression go away if the chunk size matches the IO size,
> > or if the IO size vs chunk size relationship is reversed?
> 
> According to the output below, the chunk size is 512K,

Ok.

`iostat -dxm 5` output during the fio run on both kernels will give
us some indication of the differences in IO patterns, queue depths,
etc.

Silly question: if you use DM to create the same RAID 0 array
with a dm table such as:

0 75011629056 striped 12 1024 /dev/nvme7n1 0 /dev/nvme0n1 0 ....  /dev/nvme12n1 0

to create a similar 38TB raid 0 array, do you see the same perf
degradation?

-Dave.
-- 
Dave Chinner
david at fromorbit.com