Comment 24 for bug 1668557

Theory confirmed, due to the fix the real "capable" max kb is set, that lets the block device layer merge and hold back requests. Only to later be split by the raid controller.

Following the IRC discussion using that as a tuning to "fix" is ok.

Closing as as it turned out not to be a bug.

The kernel has the proper tunable already (the one we used), but having a knob in the HW controller might be worth to avoid everybody finding that the hard way.