freebsd stable - Dec 2019 - 12.1, Dell 740 and the M2 SSD as boot media doesn't work

I tried an install on a new Dell 740, which has dual M2 256GB internal
SSD on a "Boss" controller. It exposes as AHCI.

It wouldn't recognize these as installable drives as raw devices. If
you use the Boss to define a virtual drive in RAID-1 it exposes fine.

Tried BIOS mode (not UEFI), tried FB13. No go. But, as a virtual,
worked fine in UEFI boot mode.

Dell. I mean, its not like we haven't been here before with their
special SAS firmware, but still if anyone else has seen this and knows
magic which unlocks the real device on AHCI I'd love to know.

(I actually considered using them as ARC and Cache for ZFS on the real
SAS drives but since the host doesn't "see" them as attached
devices,
I went with a h/w mirror pair to install the OS)

-G

19.12.2019 11:21, George Michaelson wrote:
> I tried an install on a new Dell 740, which has dual M2 256GB internal
> SSD on a "Boss" controller. It exposes as AHCI.
> 
> It wouldn't recognize these as installable drives as raw devices. If
> you use the Boss to define a virtual drive in RAID-1 it exposes fine.
> 
> Tried BIOS mode (not UEFI), tried FB13. No go. But, as a virtual,
> worked fine in UEFI boot mode.
> 
> Dell. I mean, its not like we haven't been here before with their
> special SAS firmware, but still if anyone else has seen this and knows
> magic which unlocks the real device on AHCI I'd love to know.
You either switch the controller to "HBA" mode using its setup
utility,
or keep it in current "RAID" mode but configure your SSD as
"Non-RAID" drive.

Also, you must use mrsas(4) driver instead of default mfi(4) to get TRIM support
for SSD.
mfi(4) has no TRIM support at all. You may switch to mrsas(4) after intallation,
though.