[Info-vax] Kittson question

[JF Mezei]

On 15-01-01 17:22, Stanley F. Quayle wrote:

> The only way for the emulated VAX to see physical DSSI devices is for a physical VAX to MSCP-serve them.

When a remote disk is served vis MSCP, does the local host use any
driver specific to that remote disk or does it use a vanilla MSCP driver
to access the disk ?

> Some people actually want to completely replace their system without changing anything (duh).

I don't think I have ever had a VAX upgrade where the disk names didn't
change. The one "half" exception was moving from RD54 to SCSI drives on
Microvax II, the SCSI adaptor emulated RA drives so they also came out
as DUAx: devices.



> So, you can make a DSSI cluster -- as I said previously, the cluster and disk access is done using IP across the host (Windows, etc.) network interface.
> It's just a question of keeping the virtual implementation the same as
the physical one was. It's actually kind of a pain to set up.

>From a technical point of view, would an application ever see a
difference ?  Would this generally result in the "fake" DSSI traffic
traveling on a separate ethernet link from SCS so that you could have
those on separate ethernets to provide some redundancy ?



> 
> CHARON-VAX can emulate any model of disk, 

>From a functional point of view, forgetting any marketing and stupid
customers who insist the disk cannot change names, is there a point in
emulating more than one disk device type ?

If you emulate DKAxxx: SCSI devices, are you able to pass the SCSI
commands directly to the harware ?  Or is that no longer desirable due
to age of the VMS SCSI drivers compared to modern SCSI protocols ?
(we're talking VAX here)


> It works just like the physical machine being emulated, which is the point.

The way I see it: when VAX was alive, people upgraded from one VAX to
the next. They didn't mind device nakes changing, they loved the ability
to have more memory and didn't really care if memory paths went from 24
to 30 bits or whatever the highest the VAX ever saw.

So I am puzzled on why people today would have a requirement to forbid
any change in the environment when "upgrading" to a newer VAX.  I guess
if they no longer have access to human resources that can do the upgrade
and change logical names etc, they really do have to maintain everything
exactly the same.

But define/system/exec DUA0 DKA200  works too in trying to provide
transparent move to a new system.