[DRBD-user] 'systemctl start drbd' resets /sys/block/sdb/queue/rotational

[Lars Ellenberg]

On Fri, Mar 22, 2019 at 10:45:52AM +0000, Holger Kiehl wrote:
> Hello,
> 
> I have megaraid controller with only SAS SSD's attached which always
> sets /sys/block/sdb/queue/rotational to 1. So, in /etc/rc.d/rc.local
> I just did a 'echo -n 0 > /sys/block/sdb/queue/rotational', that fixed
> it. But after a 'systemctl start drbd' this value gets reset back to
> 1. Any idea why this is done?

DRBD is a "new block device" for the system,
that triggers a udev run,
and udev then does more than was asked of it,
and figures that it should reset that attribute.

At least that's my educated guess.

Maybe don't work around udev (by having something in rc.local override it),
but tell udev what it should do for your non-rotational block devices.

    Lars