Re: The state of SAS

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

Lets try that again with the quoting done right :)


On 09/03/2019 23:57, Mike Pumford wrote:
> 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