Re: The state of SAS

[Mike Pumford <mpumford%mudcovered.org.uk@localhost>]

On 09/03/2019 22:57, Staffan Thomén wrote:
> Hello list
> The machine has a SuperMicro-branded LSI MegaRAID 2108 card and it works 
> fine with the mfi driver, although I don't seem to have any way of 
> configuring it from a running system (bioctl can list the volumes and 
> that's about it) which is a bit of a drag.
> Configuration is probably done through the BIOS interface. I've always 
used the cards in non-RAID mode so I'm not really sure.
> I also recently got a SAS tape drive, and connected it to the system and 
> nothing happened. This might of course be because either a) the raid 
> controller card does not support tape drives or b) they have to be 
> configured and the card bios does not do it automatically.
Its possible a card in RAID mode can't handle a stand alone device. 
Never had access to a SAS tape drive so thats outside my area of knowledge.
> My questions then are;
>
> How does SAS really work (in NetBSD); specifically tape drives? Is it 
> completely transport agnostic and st(4) will just attach?
> SAS should be fully hotplug aware so the appropriate sd/st devices 
should come and go as you plug and unplug them.

> Can I scan the scsibus and expect things Just Work like with SCSI?
Should be no need for scans the devices should just appear as they are 
plugged in. It certainly worked that way on NetBSD when I did some 
testing with a SAS disk enclosure a while back.

> What about with a non-raid HBA?
The LSI raid HBAs can usually be flashed with non-RAID firmware if you 
want to use them in that mode. I've not yet come across any generation 
of LSI card that this can't be done up to and including the current SAS3 
chips. Firmware is typically flashed with lsiutil. Not sure if that runs 
on NetBSD but it certainly does on linux so a quick boot off a live 
filesystem linux CD should let you experiment with that. lsiutil also 
provides other diagnostics like bus topology which might help work out 
why your tape drive isn't working.

Mike