10.1 RC4 r273903 - zpool scrub on ssd mirror - ahci command timeout

[Peter HEINER]

> So I now think the whole problem centers around the Samsung 850 PRO
> 512GB SSDs. Too bad I do not have the budget to just buy two Intel (or
> other) SSDs of similar size and see if the timeouts disappear..
>
> I wonder if this is a firmware issue with the drive or just some
> misguided fancy energy saving feature of this particular drive
> model causing the whole trouble.

I don't think it's the SSDs, as I'm seeing the exact same behaviour
using 4 2TB WD Reds in a raidz1 with 10.1-RELEASE on a HP N40L as well.
Whenever I do heavy reads like a scrub or send, there are CAM timeouts
and  eventually the drives detach. I had to downgrade to 10.0-RELEASE,
which seems to work fine so far. The box ran Ubuntu until recently,
without issues.
I am happy to troubleshoot further, should anyone want to pick this up.
I'm relatively new to FreeBSD, so any guidance on next steps to take is
welcome.

p