Re: Virtualized VMS in clusters (general questions)

Alan Winston - SSRL Central Computing wrote:

I'm trying to wrap my head around how virtualized VMS systems participate in
certain aspects of clustering and volume shadowing. There may be something
I'm just not getting. So this is kind of general.

When VMS boots, it asks the hardware layer (EFI in case of those IA64
things) about what devices are available.

So when HP-UX hosts an instance of VMS, you configure the HP=UX software
to give the VMS instance a list of devices it should have access to. I
assume HP-UX provides an EFI emulator which interacts with VMS and which
gives VMS the hardware config VMS will then use.

There are different ways to deal with hardware abstaction:

Use a "galaxy" style where the early boot environment gives each
instance its own list of exclusive devices and the instances deal with
the devices directly. This has the least amount of overhead because
there is no middleman to process each IO.

Use a low level intercept. VMS is told its has an EWA0: ethernet device.
When it makes a IO request to it, HP-UX intercepts it and resends it to
the actual ethernet device which would exists at the HP-UX level.
Eassentially a remapping of device name from HP-UX names to VMS names.

Another way is to have special drivers in the hosted OS which
automatically remap IO requests to the HP=UX software.

Consider how Insignia did it for hosting Windows on the old Macs:
Windows had a couple of special Insignia provided drivers. When a
Windows app wanted to connect to the internet, a special driver at the
windows level would handle those socket calls and pass them on to MacOS.
From the MACos point of view, it was getting a socket call from the
insignia application to connect to the internet. This means that you
didn't need to configure the internet connection on windows, it was
using the Mac native config. But this means that you couldn't have a web
server running on both the MAcOS and emulated Windows because they would
both try to listen to the same port 80.




.

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