Subject: Re: various scsi questions
To: Manuel Bouyer <email@example.com>
From: Matthew Jacob <firstname.lastname@example.org>
Date: 02/08/2000 14:25:32
On Tue, 8 Feb 2000, Manuel Bouyer wrote:
> in the process of builing a high-end NFS server I've ordered and alpha DS20.
> Now I have to put disks in, so a few questions to peoples who knows SCSI
> better than me:
> 1) what is really ultra2wide scsi (the one at 80MB/s) ?
This is 'Low Voltage Differential' and requires special negotiations.
> does it uses the same cables as Ultrawide ?
No. It needs those twisted pair flat cables.
> Can I mix ultra2wide and ltrawide on the same bus ?
> (I've never looked at ultra2wide scsi devices yet :)
> 2) with a dual-channel scsi board, do we have twice the bandwidth (i.e. can
> the controller manage I/O from both channels at the same time) ?
It depends on the board and how it's arranged, whether it's bridged and
whether it has FIFOing...
Note that 80MB/s (or 160MB/s for Ultra3- I'm about to check in support for
this) is still only in DATA PHASE. Command/Status/Message phases are still
async mode. With Fibre Channel, you get maybe nearly twice the effective IOPs
because command/status stuff gets shipped at the same data rate as data
> 3) which scsi board would you use (supported in -current or in the near future
> of course :) ? I'd prefer 64bits PCI boards, and PCI slots usage may be an
> issue so dual-channel boards may be an option if it's worth it (I think
> I'll need 4 scsi busses in this machine).
The Qlogic 1280 is supported and works pretty well- this is a dual LVD board.
It's close to impossible to buy them as an end user, thouugh. The 12160
(Ultra3) board is just about to be supported.
The ncr driver claims to support the 895/896(dual) LVD boards, but have no
faith in this driver and have not tested it against LVD cards at all.
There may or may not be support for the Adaptec LVD cards coming into NetBSD