OpenVMS on x86 and Virtual Machines -- An Observation

[g***@rlgsc.com]

While attending the Oracle-hosted OpenVMS Update in New York City this past Monday, I realized that there was a potential for misconception and misunderstanding.

Traditionally, OpenVMS has been run on dedicated hardware. In the past two decades, an initially small but increasing number of systems have been, and are, running on one or another emulator (e.g., simh, Charon, AVT, etc.). With the advent of OpenVMS on x86, there is an increasing discussion of running OpenVMS x86 on various virtual machine hypervisors (e.g., xen, VirtualBox, Hyper-V).

Questions ensue along the lines of "What if my (fill in your supported VM) infrastructure is using enterprise-class storage facility that is not supported by OpenVMS?"

What matters in a hypervisor-based environment is not the underlying storage or network device used by the hypervisor. What does matter is the simulated device presented to the client virtual machine.

For example, if one is using VirtualBox in concert with a brand X storage array, it does not matter if the brand X storage array is supported by OpenVMS. What matters is the that the virtual storage device presented to the x86 virtual machine instance running OpenVMS is a device supported by OpenVMS.

Using currently available products, it is essentially the same situation as the RDxx or RAxx series device simulations provided by Charon, AVT, and other emulation products. The simulated environment is one thing, the actual underlying technology is something else entirely.

Thus, if your long-term plans are to run OpenVMS x86 on a hypervisor-based infrastructure, the peripheral support matrices need to be examined in a different light than has been relevant in the past.

- Bob Gezelter, http://www.rlgsc.com

[Stephen Hoffman]

Post by g***@rlgsc.com
While attending the Oracle-hosted OpenVMS Update in New York City this
past Monday, I realized that there was a potential for misconception
and misunderstanding.
Traditionally, OpenVMS has been run on dedicated hardware. In the past
two decades, an initially small but increasing number of systems have
been, and are, running on one or another emulator (e.g., simh, Charon,
AVT, etc.). With the advent of OpenVMS on x86, there is an increasing
discussion of running OpenVMS x86 on various virtual machine
hypervisors (e.g., xen, VirtualBox, Hyper-V).
Questions ensue along the lines of "What if my (fill in your supported
VM) infrastructure is using enterprise-class storage facility that is
not supported by OpenVMS?"
What matters in a hypervisor-based environment is not the underlying
storage or network device used by the hypervisor. What does matter is
the simulated device presented to the client virtual machine.
...........

As with the rest of this business, "it depends".

At one end of the spectrum, there's full-on virtualization. This is
where the guest operating system is oblivious to the presence of
virtualization, and accesses fully virtualized devices. This adds some
overhead, as the virtual machine hypervisor has to present a device
interface and host environment that the guest supports, and there's
some overhead in that mapping within the hypervisor. Few or no guest
modifications are required, depending on how close the virtualization
presents the hardware. And in this design and as Bob indicates, the
guest of the hypervisor is oblivious to what sorts of storage is
located behind the hypervisor.

At the other end of the spectrum, there's hardware pass-through akin to
what OpenVMS Galaxy provided on Alpha. Where the virtual machine
coordinates which guests can access which hardware devices in the
underlying configuration, and each guest accesses its own hardware
subset and its allocated hardware devices directly. This avoids the
overhead of the intermediate layer that's involved with full-on
virtualization within the hypervisor. With the subset ACPI hardware
configuration data presented from the hypervisor and the existing
drivers, the guest can connect and use guest-specific device drivers
directly. Few or no guest modifications are required.

In the middle, there's what's called paravirtualization, where the
guest is modified to provide drivers into the emulation. This is akin
to the UQSSP interface from aeons past, and the SCSI command sets used
on more recent SCSI, SAS, SATA and related devices. Where the guest
operating system communicates via an API presented by the virtual
machine. This requires guest modifications, but it can provide much
better performance than the overhead of emulating hardware devices
through software within the virtual machine. This is the preferred
path, though it does mean the guest must detect and support the
hypervisor and its associated API.

The paravirtualization support can vary widely, too. At its simplest,
it'll be akin to a VAX emulator that has chosen to implement the
architected VAX idle instruction (02FD WAIT Wait for Interrupt) or
similar as a way to allow a slightly-modified guest to signal its idle
state to the emulator (or to the hypervisor), without requiring the
emulator (or the hypervisor) to detect the guest idle loop. Or the
communications and coordination between the guest and the hypervisor
can be far more involved.

Beyond the presentation of the I/O interfaces, a particular hypervisor
can virtualize processors, memory and other system resources.

And emulation has opened up with some very different approaches, with
apps and with whole operating systems compiled into and targeting Wasm
and ilk, with intermediate approaches akin to Bitcode, and with
projects such as Klee.

The other wrinkle in this discussion is the supported hypervisor, as
various folks have specific requirements for hypervisors. VSI has a
working list of hypervisors they're targeting, though that list may
well evolve as the port proceeds. One detail that has been discussed,
though: and the vendor of one of the more common
hypervisors—VMware—will not be supporting OpenVMS as a guest. The lack
of VMware support been discussed before, and it'll be discussed again.
Now as to whether OpenVMS boots and runs under VMware, unsupported?
That's a different discussion.


Here's an intro to virtualization, and there are many others available...
http://dsc.soic.indiana.edu/publications/virtualization.pdf
https://binarydebt.wordpress.com/2018/10/14/intel-virtualisation-how-vt-x-kvm-and-qemu-work-together/


For some discussions around virtualization and security...
https://www.qubes-os.org/intro/
https://developer.amd.com/sev/
https://blog.cloudflare.com/cloud-computing-without-containers/
(Wasm-based; also see
https://groups.google.com/d/msg/comp.os.vms/6nQ1oSo9zNc/RS-6IPcMBQAJ )
https://googleprojectzero.blogspot.com/2017/04/pandavirtualization-exploiting-xen.html

https://df-stream.com/2017/08/memory-acquisition-and-virtual-secure/

Bitcode:
https://lowlevelbits.org/bitcode-demystified/

And just for grins, since LLVM is soon (finally) in play on OpenVMS...
https://klee.github.io



OpenVMS has been in a backwater for quite a while, around the
associated hardware and software environments and tools.

[Phillip Helbig (undress to reply)]

Post by g***@rlgsc.com
Traditionally, OpenVMS has been run on dedicated hardware.
With the advent of OpenVMS on x86, there is an increasing discussion of
running OpenVMS x86 on various virtual machine hypervisors

Since VMS will soon run natively on x86, what is the motivation to run
it on some sort of emulator?

[Craig A. Berry]

Post by Phillip Helbig (undress to reply)

Post by g***@rlgsc.com
Traditionally, OpenVMS has been run on dedicated hardware.
With the advent of OpenVMS on x86, there is an increasing discussion of
running OpenVMS x86 on various virtual machine hypervisors

Since VMS will soon run natively on x86, what is the motivation to run
it on some sort of emulator?

A hypervisor is not an emulator. As far as why run on a virtual
machine, it's the same reason that most instances of most operating
systems that run natively on x86 these days run on virtual machines.
Mostly configuration and management flexibility, some DR operations,
etc. VMS would only be different where it lacks capabilities to take
advantage of the virtualization environment.

[g***@rlgsc.com]

Post by Phillip Helbig (undress to reply)

Post by g***@rlgsc.com
Traditionally, OpenVMS has been run on dedicated hardware.
With the advent of OpenVMS on x86, there is an increasing discussion of
running OpenVMS x86 on various virtual machine hypervisors

Since VMS will soon run natively on x86, what is the motivation to run
it on some sort of emulator?

Phillip,

Not an emulator. Under a hypervisor.

Many organizations have gone to an infrastructure based upon blades and SANs. While it is possible to provision physical hardware in such configurations, the most prevalent allocation strategy is to provision virtual machine instances, which are mapped to full/fractional shares of physical hardware. In such a configuration, one is often not able to run on bare hardware.

The program that manages the real hardware in such a configuration is referred to as a hypervisor. Strictly speaking, a hypervisor is a virtual machine manager, providing a protection between virtual machines, but not changing the underlying instruction set. An x86 virtual machine still runs the x86 instruction set.

An emulator provides for a different instruction set (e.g., VAX, Alpha) than the underlying hardware. This generally involves some form of translation on the fly.

- Bob Gezelter, http://www.rlgsc.com

[Bill Gunshannon]

Post by Phillip Helbig (undress to reply)

Post by g***@rlgsc.com
Traditionally, OpenVMS has been run on dedicated hardware.
With the advent of OpenVMS on x86, there is an increasing discussion of
running OpenVMS x86 on various virtual machine hypervisors

Since VMS will soon run natively on x86, what is the motivation to run
it on some sort of emulator?

virtual machine hypervisors != emulators

bill

[Stephen Hoffman]

Post by Phillip Helbig (undress to reply)
Since VMS will soon run natively on x86, what is the motivation to run
it on some sort of emulator?

Emulation involves differing instruction sets and differing
architectures and run-time instruction translation. The underlying
hardware is typically of a different architecture with a different
instruction set.

Apps and operating systems running under virtualization use the native
instruction set and architecture of the hardware with no translations,
and with a few specific operations either invoking the hypervisor or
reserved to the hypervisor. Outside of those operations, instructions
and apps run at full speed, untranslated, directly on the underlying
hardware.

For you? Maybe you'll be running parts of your environment under
virtualization eventually, as it'll let you build and test different
environments—multiple instances of OpenVMS, and mixes of OpenVMS and
other operating systems—on the same hardware. That might well involve
a OpenVMS cluster operating within a single box for instance, while
you're migrating your plethora of old Alpha hardware to fewer or
potentially to one x86-64 box. You may well find that a single small
x86-64 box runs your entire existing Alpha load, after all. Or you
might eventually be testing a newer product release or a newer
installation of OpenVMS, without disrupting the main installation.
Getting your entire environment upgraded to the VSI releases for Alpha,
and then clustering with the x86-64 boxes and getting your apps ported.

For other folks, virtualization means that their OpenVMS apps can be
hosted on a shared server, and that folks can boot up multiple OpenVMS
instances for unexpected loads. This is consolidating hardware to
fewer boxes, and this can also involve temporarily renting hardware and
software rather than the expense of purchase what may well be excessive
hardware and software capacity. If you're running a back-end for a
gaming environment, you can either purchase enough hardware for your
maximum load and hope that some extremely-popular game doesn't exceed
that capacity, and also hope that the aggregate load can support the
costs of what can often be excess capacity. It also means that folks
don't necessarily have to staff as many data centers, and can boot up
hosts that are geographically local to the clients. Or geographically
appropriately-distant, in the case of disaster preparedness. Etc.

Rolling in a system image—a fully-configured environment—and booting it
as needed is pretty handy for deployment, testing, and for recovery,
too. With virtualization, it's possible to effectively pause the whole
running environment out to disk, transfer it to another host, reload
the guest onto another hypervisor on another box, and restart the
paused processing.

Some organizations outsource the hosting for their servers, and other
folks prefer to have their own shared data centers and shared hosting.

Can you do this with hardware? Sure. But you're going to be
purchasing a whole lot of capacity you won't be using, if you don't
want to saturate. And moving copies of guests is easier than moving
backups around.

I routinely have guests running on the local desktop box, as that
allows me to use apps and tools that require specific Linux or BSD
distributions. I don't need to reboot, or switch to other hosts, or to
even need or use additional hardware to do this.

For some of the parallels here with virtualized hosts, ponder what
virtualized memory and virtualized storage and virtualized networking
have each provided.

[Dave Froble]

Post by Stephen Hoffman

Post by Phillip Helbig (undress to reply)
Since VMS will soon run natively on x86, what is the motivation to run
it on some sort of emulator?

Emulation involves differing instruction sets and differing
architectures and run-time instruction translation. The underlying
hardware is typically of a different architecture with a different
instruction set.
Apps and operating systems running under virtualization use the native
instruction set and architecture of the hardware with no translations,
and with a few specific operations either invoking the hypervisor or
reserved to the hypervisor. Outside of those operations, instructions
and apps run at full speed, untranslated, directly on the underlying
hardware.
For you? Maybe you'll be running parts of your environment under
virtualization eventually, as it'll let you build and test different
environments—multiple instances of OpenVMS, and mixes of OpenVMS and
other operating systems—on the same hardware. That might well involve a
OpenVMS cluster operating within a single box for instance, while you're
migrating your plethora of old Alpha hardware to fewer or potentially to
one x86-64 box. You may well find that a single small x86-64 box runs
your entire existing Alpha load, after all. Or you might eventually be
testing a newer product release or a newer installation of OpenVMS,
without disrupting the main installation. Getting your entire
environment upgraded to the VSI releases for Alpha, and then clustering
with the x86-64 boxes and getting your apps ported.
For other folks, virtualization means that their OpenVMS apps can be
hosted on a shared server, and that folks can boot up multiple OpenVMS
instances for unexpected loads. This is consolidating hardware to fewer
boxes, and this can also involve temporarily renting hardware and
software rather than the expense of purchase what may well be excessive
hardware and software capacity. If you're running a back-end for a
gaming environment, you can either purchase enough hardware for your
maximum load and hope that some extremely-popular game doesn't exceed
that capacity, and also hope that the aggregate load can support the
costs of what can often be excess capacity. It also means that folks
don't necessarily have to staff as many data centers, and can boot up
hosts that are geographically local to the clients. Or geographically
appropriately-distant, in the case of disaster preparedness. Etc.
Rolling in a system image—a fully-configured environment—and booting it
as needed is pretty handy for deployment, testing, and for recovery,
too. With virtualization, it's possible to effectively pause the whole
running environment out to disk, transfer it to another host, reload the
guest onto another hypervisor on another box, and restart the paused
processing.
Some organizations outsource the hosting for their servers, and other
folks prefer to have their own shared data centers and shared hosting.
Can you do this with hardware? Sure. But you're going to be purchasing
a whole lot of capacity you won't be using, if you don't want to
saturate. And moving copies of guests is easier than moving backups
around.
I routinely have guests running on the local desktop box, as that allows
me to use apps and tools that require specific Linux or BSD
distributions. I don't need to reboot, or switch to other hosts, or to
even need or use additional hardware to do this.
For some of the parallels here with virtualized hosts, ponder what
virtualized memory and virtualized storage and virtualized networking
have each provided.

Many good reasons to have the VM capability. However, don't lay it on
too thick. When talking about capacity, TANSTAAFL, spinning up another
guest on HW that is already running at max isn't going to give you any
more capacity. Probably less.

I really should start getting some experience with VMs. Any suggestions
for good ones for a beginner to learn? Is using WEENDOZE to run the VM
Ok? Or do I need to learn to run some Linux? Which one?

[g***@rlgsc.com]

Post by Dave Froble

Post by Stephen Hoffman

Post by Phillip Helbig (undress to reply)
Since VMS will soon run natively on x86, what is the motivation to run
it on some sort of emulator?

Emulation involves differing instruction sets and differing
architectures and run-time instruction translation. The underlying
hardware is typically of a different architecture with a different
instruction set.
Apps and operating systems running under virtualization use the native
instruction set and architecture of the hardware with no translations,
and with a few specific operations either invoking the hypervisor or
reserved to the hypervisor. Outside of those operations, instructions
and apps run at full speed, untranslated, directly on the underlying
hardware.
For you? Maybe you'll be running parts of your environment under
virtualization eventually, as it'll let you build and test different
environments—multiple instances of OpenVMS, and mixes of OpenVMS and
other operating systems—on the same hardware. That might well involve a
OpenVMS cluster operating within a single box for instance, while you're
migrating your plethora of old Alpha hardware to fewer or potentially to
one x86-64 box. You may well find that a single small x86-64 box runs
your entire existing Alpha load, after all. Or you might eventually be
testing a newer product release or a newer installation of OpenVMS,
without disrupting the main installation. Getting your entire
environment upgraded to the VSI releases for Alpha, and then clustering
with the x86-64 boxes and getting your apps ported.
For other folks, virtualization means that their OpenVMS apps can be
hosted on a shared server, and that folks can boot up multiple OpenVMS
instances for unexpected loads. This is consolidating hardware to fewer
boxes, and this can also involve temporarily renting hardware and
software rather than the expense of purchase what may well be excessive
hardware and software capacity. If you're running a back-end for a
gaming environment, you can either purchase enough hardware for your
maximum load and hope that some extremely-popular game doesn't exceed
that capacity, and also hope that the aggregate load can support the
costs of what can often be excess capacity. It also means that folks
don't necessarily have to staff as many data centers, and can boot up
hosts that are geographically local to the clients. Or geographically
appropriately-distant, in the case of disaster preparedness. Etc.
Rolling in a system image—a fully-configured environment—and booting it
as needed is pretty handy for deployment, testing, and for recovery,
too. With virtualization, it's possible to effectively pause the whole
running environment out to disk, transfer it to another host, reload the
guest onto another hypervisor on another box, and restart the paused
processing.
Some organizations outsource the hosting for their servers, and other
folks prefer to have their own shared data centers and shared hosting.
Can you do this with hardware? Sure. But you're going to be purchasing
a whole lot of capacity you won't be using, if you don't want to
saturate. And moving copies of guests is easier than moving backups
around.
I routinely have guests running on the local desktop box, as that allows
me to use apps and tools that require specific Linux or BSD
distributions. I don't need to reboot, or switch to other hosts, or to
even need or use additional hardware to do this.
For some of the parallels here with virtualized hosts, ponder what
virtualized memory and virtualized storage and virtualized networking
have each provided.

Many good reasons to have the VM capability. However, don't lay it on
too thick. When talking about capacity, TANSTAAFL, spinning up another
guest on HW that is already running at max isn't going to give you any
more capacity. Probably less.
I really should start getting some experience with VMs. Any suggestions
for good ones for a beginner to learn? Is using WEENDOZE to run the VM
Ok? Or do I need to learn to run some Linux? Which one?
--
David Froble Tel: [phone]
DFE Ultralights, Inc.
170 Grimplin Road
Vanderbilt, PA 15486

David,

VirtualBox runs quite nicely on an appropriate notebook. I have often used it for when I need a Linux system for one thing or another. As an additional benefit, it is completely portable, no network link needed to gain access.

One of the nice things about VM provisioning is the ease of creating expendable test systems. Cloning a system to do a potentially dangerous test? Less than a minute on my laptop. Need to run a piece of dicey software. Bring up a VM with cloned mass storage.

Many have observed that creating a virtual instance is the work of seconds. Procuring and installing hardware takes hours if not days or longer. The cost of creating/destroying virtual instances is pennies compared to tens of thousands US$. Check out what Amazon charges for a non-dedicated instance. Pocket change. I have seen university faculty tell students to create Amazon instances for courses rather than go through the university.

- Bob Gezelter, http://www.rlgsc.com

[Stephen Hoffman]

Post by Dave Froble
I really should start getting some experience with VMs. Any
suggestions for good ones for a beginner to learn? Is using WEENDOZE
to run the VM Ok? Or do I need to learn to run some Linux? Which one?

To get started? To learn? Run what you have.

Microsoft Hyper-V is part of the Windows 8 Pro and higher-spec
packages, and of later Windows Pro and higher-spec packages.

VSI has discussed Xen, kvm and VirtualBox and those on Linux, though
that list may well vary.

VirtualBox runs on various platforms.

Beyond the emulator, Linux and Unix is knowledge can be useful, though
it's a fair jump from Windows and OpenVMS.

Linux scale and scope and tooling is far past OpenVMS, too.

Windows Services for Linux (WSL) can be a reasonable introduction to
Linux on Windows 10.

Or booted as a guest in a hypervisor, of course.

Lots of options for Linux distros. Lots of opinions here, too.

Local Linux use is primarily Kali, with some interest in Black Arch and
Arch Linux. Those are not for what you're doing, though.

Local preference is for BSD distros, and particularly for macOS for client.

macOS can provide a fairly gentle introduction to Unix, and to newer
development tools, languages and approaches.

I've worked with VirtualBox, VMware Fusion and Parallels Desktop on
macOS, and with some other VMs. There are options.

If you want to tie into VMware and its tooling on macOS, then Fusion.
That's not something you'll be interested quite yet, though.

And there'll be some frustration, whenever learning something new and
different.

[Arne Vajhøj]

I really should start getting some experience with VMs.  Any suggestions
for good ones for a beginner to learn?  Is using WEENDOZE to run the VM
Ok?  Or do I need to learn to run some Linux?  Which one?

There are plenty available for both Linux and Windows.

For Windows some of the options are:
* Microsoft Windows Virtual PC (free)
* Oracle VirtualBox (free, but note that the extension pack is not)
* VMware Workstation Player (free for non-commercial usage)

There is a list on Wikipedia:

https://en.wikipedia.org/wiki/Comparison_of_platform_virtualization_software

Arne

[Arne Vajhøj]

I really should start getting some experience with VMs.  Any suggestions
for good ones for a beginner to learn?  Is using WEENDOZE to run the VM
Ok?  Or do I need to learn to run some Linux?  Which one?

If you want to learn Linux then I would suggest CentOS.

"server mentality"

100% compatible with Redhat Linux which makes the skills
you learn business relevant.

Arne

[Robert A. Brooks]

Post by Arne Vajhøj

Post by Dave Froble
I really should start getting some experience with VMs. Any
suggestions for good ones for a beginner to learn? Is using
WEENDOZE to run the VM Ok? Or do I need to learn to run some
Linux? Which one?

If you want to learn Linux then I would suggest CentOS.
"server mentality"
100% compatible with Redhat Linux which makes the skills you learn
business relevant.

For the handful of Linux systems we have at VSI, we use CentOS.

[IanD]

CentOS is loved because it's the free arm of redhat

David, VM's are addictive, once you try them out you'll love and appreciate the flexibility they bring

Sure, there's some fun about learning various switches and unique configuration setting on hardware panels but as get older that fun slowly fades and your left just wanting to get a job done

Virtualbox is ok and had got better. VMware workstation used to be awesome until they fired all the developers and did the development offshore somewhere.

You could always sign up for something like AWS or azure free tier (you basically get a year for free) and play with spinning up and down instances. AWS makes it very easy.
There plenty of YouTube videos walking you through the process

After playing with VM's you'll start to feel somewhat frustrated when you go back to physical hardware, but that's it's terrible, it's just that VM's open up an order of flexibility that you don't realise you missed because you never had it :-)

[David Wade]

Post by IanD
CentOS is loved because it's the free arm of redhat
David, VM's are addictive, once you try them out you'll love and appreciate the flexibility they bring
Sure, there's some fun about learning various switches and unique configuration setting on hardware panels but as get older that fun slowly fades and your left just wanting to get a job done
Virtualbox is ok and had got better. VMware workstation used to be awesome until they fired all the developers and did the development offshore somewhere.
You could always sign up for something like AWS or azure free tier (you basically get a year for free) and play with spinning up and down instances. AWS makes it very easy.
There plenty of YouTube videos walking you through the process
After playing with VM's you'll start to feel somewhat frustrated when you go back to physical hardware, but that's it's terrible, it's just that VM's open up an order of flexibility that you don't realise you missed because you never had it :-)

I also think that if you have a spare box it might be worth loading the
VMWARE vsphere which is a bare metal hypervisor. I think you can still
get a free copy...

Dave

[IanD]

Older versions of esxi are free too. I think it's normally current minus 1 version?

But you need to check the hardware requirements, it strictly only supports certain hardware configurations. Raid cards typically stop most people who try and just use an old PC

I got myself a couple of HP Microservers a while back, put esxi on and then windows and an alpha emulator as ran a small VMS 8.4 hobbyists cluster to play around with. Great for learning about VMware stuff and of course playing around with a VMS cluster was fun

Very good for playing with and learning about stuff. Disk activities were slow (just used SATA drives) and memory limitations of the microserver meant only 2 or 3 VMS systems per microserver. Some of the emulators we're too limited

The nice thing about a microserver was that HP produced esxi images so you didn't have to stuff around with trying to obtain specific drivers. Their esxi imagine contained all the driver's for their microserver

The low power consumption of the microserver meant I just left them on. They booted from USB which eventually became a pita because esxi under certain conditions involving power fluctuations would corrupt the keyboard driver so 1 time in about 20, you would have a boot issue. This setup was about as low budget as one could go so some hiccups were to be expected. But it did get tiresome and now I haven't bothered booting any of it in over 1 1/2 years and now that I don't work with VMS anymore, there's even less incentive.
I also gave up waiting for VSI to bring out a hobbyist license :-(

[Andy Burns]

Post by IanD
Older versions of esxi are free too. I think it's normally current minus 1 version?

ctually, even the current version is free, but you don't get any of the
vsphere management features, so you have to manage each box individually
and can't do any of the "fancy" stuff such as live migration of VMs
between boxes, or failover.

[Dave Froble]

Post by David Wade

Post by IanD
CentOS is loved because it's the free arm of redhat
David, VM's are addictive, once you try them out you'll love and
appreciate the flexibility they bring
Sure, there's some fun about learning various switches and unique
configuration setting on hardware panels but as get older that fun
slowly fades and your left just wanting to get a job done
Virtualbox is ok and had got better. VMware workstation used to be
awesome until they fired all the developers and did the development
offshore somewhere.
You could always sign up for something like AWS or azure free tier
(you basically get a year for free) and play with spinning up and down
instances. AWS makes it very easy.
There plenty of YouTube videos walking you through the process
After playing with VM's you'll start to feel somewhat frustrated when
you go back to physical hardware, but that's it's terrible, it's just
that VM's open up an order of flexibility that you don't realise you
missed because you never had it :-)

I also think that if you have a spare box it might be worth loading the
VMWARE vsphere which is a bare metal hypervisor. I think you can still
get a free copy...
Dave

Thanks, I'm going top do that. Maybe better than running on top of
WEENDOZE.

[Dave Froble]

Post by David Wade

Post by IanD
CentOS is loved because it's the free arm of redhat
David, VM's are addictive, once you try them out you'll love and
appreciate the flexibility they bring
Sure, there's some fun about learning various switches and unique
configuration setting on hardware panels but as get older that fun
slowly fades and your left just wanting to get a job done
Virtualbox is ok and had got better. VMware workstation used to be
awesome until they fired all the developers and did the development
offshore somewhere.
You could always sign up for something like AWS or azure free tier
(you basically get a year for free) and play with spinning up and down
instances. AWS makes it very easy.
There plenty of YouTube videos walking you through the process
After playing with VM's you'll start to feel somewhat frustrated when
you go back to physical hardware, but that's it's terrible, it's just
that VM's open up an order of flexibility that you don't realise you
missed because you never had it :-)

I also think that if you have a spare box it might be worth loading the
VMWARE vsphere which is a bare metal hypervisor. I think you can still
get a free copy...
Dave

I thought this was a good idea. Got the boot ISO file, created DVD, and
loaded.

It complained that there was no network card, or it was not recognized.
No info on how to load custom driver, which came with motherboard.

Can I assume that I cannot use this system for evaluation of the hypervisor?

[Dave Froble]

Post by IanD
CentOS is loved because it's the free arm of redhat
David, VM's are addictive, once you try them out you'll love and appreciate the flexibility they bring
Sure, there's some fun about learning various switches and unique configuration setting on hardware panels but as get older that fun slowly fades and your left just wanting to get a job done
Virtualbox is ok and had got better. VMware workstation used to be awesome until they fired all the developers and did the development offshore somewhere.
You could always sign up for something like AWS or azure free tier (you basically get a year for free) and play with spinning up and down instances. AWS makes it very easy.
There plenty of YouTube videos walking you through the process
After playing with VM's you'll start to feel somewhat frustrated when you go back to physical hardware, but that's it's terrible, it's just that VM's open up an order of flexibility that you don't realise you missed because you never had it :-)

Well, I downloaded Virtual Box V6.??, and tried to install it on a 32
bit Win XP box. No luck, it needs 64 bit WEENDOZE.

I had a V4.2.? I must have downloaded in the past. No longer supported,
but, I doubt it stopped working just because it's no longer supported.
Installed fine on the box.

Created a new VM. Then loaded 32 bit WEENDOZE 7 on it. That seems to
almost work Ok. I'm having a problem getting the VM instance to see
other computers on my network. Playing with it, I may have made things
worse. Oh, well, that's what learning is all about.

I have a newer system, with 32 bit WEENDOZE 7 that I use when I need to
test TLS V1.2. Other than that, I really don't like the newer versions.
Something about "old dog" and "new tricks" I guess.

My current plan is to install WEENDOZE 7 64 bit on the newer system, and
I think I'll need to get lots more memory, and more disk space. Always
wondered what someone would do with hundreds, or thousands, of GB of
storage. Now I know at least one reason. A reason for more memory too.

I'm figuring then I can create multiple VM instances, and build various
OSs on them. One problem with newer HW is that there are few if any
drivers for WEENDOZE XP that the newer HW requires. Now, perhaps, I'll
be able to run older stuff on the newer HW, in VM instances. Hmmm, is
"instances" the correct name for the multiple VMs? Maybe even MS-DOS?
Or WEENDOZE 95?

Same as VMS will be able to run on HW for which it has no drivers, huh?

I'll toy around with the stuff for a bit, then set up the "real" VMs.

A question, does anyone know if I can take an existing system and move
it to a VM? I'm guessing I can "export" stuff to another system. But I
might want to keep some older stuff without having to re-install everything.

Another recent thing I've done is acquire a network based storage box,
and set up two 500 GB disks in a RAID 1 array. The thought is to keep
just about all of "my" stuff on that box, and the "computers" will have
just the OS and re-loadable apps. The box has a USB port, and I do a
weekly backup to a one TB USB disk. Plenty of storage for me, for now.

So, I can envision one storage box for all VM instances. Sound reasonable?

One problem, it's a bit like "work" and I don't like "work" anymore.

[Jan-Erik Söderholm]

Post by IanD
CentOS is loved because it's the free arm of redhat
David, VM's are addictive, once you try them out you'll love and
appreciate the flexibility they bring
Sure, there's some fun about learning various switches and unique
configuration setting on hardware panels but as get older that fun slowly
fades and your left just wanting to get a job done
Virtualbox is ok and had got better. VMware workstation used to be
awesome until they fired all the developers and did the development
offshore somewhere.
You could always sign up for something like AWS or azure free tier (you
basically get a year for free) and play with spinning up and down
instances. AWS makes it very easy.
There plenty of YouTube videos walking you through the process
After playing with VM's you'll start to feel somewhat frustrated when you
go back to physical hardware, but that's it's terrible, it's just that
VM's open up an order of flexibility that you don't realise you missed
because you never had it :-)

Well, I downloaded Virtual Box V6.??, and tried to install it on a 32 bit
Win XP box.  No luck, it needs 64 bit WEENDOZE.
I had a V4.2.? I must have downloaded in the past.  No longer supported,
but, I doubt it stopped working just because it's no longer supported.
Installed fine on the box.
Created a new VM.  Then loaded 32 bit WEENDOZE 7 on it.  That seems to
almost work Ok.  I'm having a problem getting the VM instance to see other
computers on my network.  Playing with it, I may have made things worse.
Oh, well, that's what learning is all about.
I have a newer system, with 32 bit WEENDOZE 7 that I use when I need to
test TLS V1.2.  Other than that, I really don't like the newer versions.
 Something about "old dog" and "new tricks" I guess.
My current plan is to install WEENDOZE 7 64 bit on the newer system, and I
think I'll need to get lots more memory, and more disk space.  Always
wondered what someone would do with hundreds, or thousands, of GB of
storage.  Now I know at least one reason.  A reason for more memory too.
I'm figuring then I can create multiple VM instances, and build various OSs
on them.  One problem with newer HW is that there are few if any drivers
for WEENDOZE XP that the newer HW requires.  Now, perhaps, I'll be able to
run older stuff on the newer HW, in VM instances.  Hmmm, is "instances" the
correct name for the multiple VMs?  Maybe even MS-DOS? Or WEENDOZE 95?
Same as VMS will be able to run on HW for which it has no drivers, huh?
I'll toy around with the stuff for a bit, then set up the "real" VMs.
A question, does anyone know if I can take an existing system and move it
to a VM?  I'm guessing I can "export" stuff to another system.  But I might
want to keep some older stuff without having to re-install everything.
Another recent thing I've done is acquire a network based storage box, and
set up two 500 GB disks in a RAID 1 array.  The thought is to keep just
about all of "my" stuff on that box, and the "computers" will have just the
OS and re-loadable apps.  The box has a USB port, and I do a weekly backup
to a one TB USB disk.  Plenty of storage for me, for now.
So, I can envision one storage box for all VM instances.  Sound reasonable?
One problem, it's a bit like "work" and I don't like "work" anymore.

FWIW...

I have Win10 64bit on my laptop. To be able to support and change
two old VB6 applications (the VB6 dev environment has some issues on
win10) I installed Virtual Box, created an instance, installed WinXP
(directly from the original CD to the new VM instance) and then
installed the VB6 IDE there. Worked just fine. All files are
accessable from both the WinXP and Win10 environments.

The Win XP environment as such is just one single container file from
the host, but the VM also has access to the hosts files, so the VB6
application is stored in the Win10 file system even though the IDE is
running in the WinXP VM. Easy to move the EXE to the target systems.

[Jan-Erik Söderholm]

Post by Jan-Erik Söderholm

Post by IanD
CentOS is loved because it's the free arm of redhat
David, VM's are addictive, once you try them out you'll love and
appreciate the flexibility they bring
Sure, there's some fun about learning various switches and unique
configuration setting on hardware panels but as get older that fun
slowly fades and your left just wanting to get a job done
Virtualbox is ok and had got better. VMware workstation used to be
awesome until they fired all the developers and did the development
offshore somewhere.
You could always sign up for something like AWS or azure free tier (you
basically get a year for free) and play with spinning up and down
instances. AWS makes it very easy.
There plenty of YouTube videos walking you through the process
After playing with VM's you'll start to feel somewhat frustrated when
you go back to physical hardware, but that's it's terrible, it's just
that VM's open up an order of flexibility that you don't realise you
missed because you never had it :-)

Well, I downloaded Virtual Box V6.??, and tried to install it on a 32 bit
Win XP box.  No luck, it needs 64 bit WEENDOZE.
I had a V4.2.? I must have downloaded in the past.  No longer supported,
but, I doubt it stopped working just because it's no longer supported.
Installed fine on the box.
Created a new VM.  Then loaded 32 bit WEENDOZE 7 on it.  That seems to
almost work Ok.  I'm having a problem getting the VM instance to see
other computers on my network.  Playing with it, I may have made things
worse. Oh, well, that's what learning is all about.
I have a newer system, with 32 bit WEENDOZE 7 that I use when I need to
test TLS V1.2.  Other than that, I really don't like the newer versions.
  Something about "old dog" and "new tricks" I guess.
My current plan is to install WEENDOZE 7 64 bit on the newer system, and
I think I'll need to get lots more memory, and more disk space.  Always
wondered what someone would do with hundreds, or thousands, of GB of
storage.  Now I know at least one reason.  A reason for more memory too.
I'm figuring then I can create multiple VM instances, and build various
OSs on them.  One problem with newer HW is that there are few if any
drivers for WEENDOZE XP that the newer HW requires.  Now, perhaps, I'll
be able to run older stuff on the newer HW, in VM instances.  Hmmm, is
"instances" the correct name for the multiple VMs?  Maybe even MS-DOS? Or
WEENDOZE 95?
Same as VMS will be able to run on HW for which it has no drivers, huh?
I'll toy around with the stuff for a bit, then set up the "real" VMs.
A question, does anyone know if I can take an existing system and move it
to a VM?  I'm guessing I can "export" stuff to another system.  But I
might want to keep some older stuff without having to re-install everything.
Another recent thing I've done is acquire a network based storage box,
and set up two 500 GB disks in a RAID 1 array.  The thought is to keep
just about all of "my" stuff on that box, and the "computers" will have
just the OS and re-loadable apps.  The box has a USB port, and I do a
weekly backup to a one TB USB disk.  Plenty of storage for me, for now.
So, I can envision one storage box for all VM instances.  Sound reasonable?
One problem, it's a bit like "work" and I don't like "work" anymore.

FWIW...
I have Win10 64bit on my laptop. To be able to support and change
two old VB6 applications (the VB6 dev environment has some issues on
win10) I installed Virtual Box, created an instance, installed WinXP
(directly from the original CD to the new VM instance) and then
installed the VB6 IDE there. Worked just fine. All files are
accessable from both the WinXP and Win10 environments.

Well, the files within the VM container file are not accessable
directly from the Win10 host, but the VM has access to a couple of
shared folders where the application are stored. Just the usual
"connect to remote folder" from WinXP to Win10...

Post by Jan-Erik Söderholm
The Win XP environment as such is just one single container file from
the host, but the VM also has access to the hosts files, so the VB6
application is stored in the Win10 file system even though the IDE is
running in the WinXP VM. Easy to move the EXE to the target systems.

[Craig A. Berry]

Post by Jan-Erik Söderholm

Post by Jan-Erik Söderholm
I have Win10 64bit on my laptop. To be able to support and change
two old VB6 applications (the VB6 dev environment has some issues on
win10) I installed Virtual Box, created an instance, installed WinXP
(directly from the original CD to the new VM instance) and then
installed the VB6 IDE there. Worked just fine. All files are
accessable from both the WinXP and Win10 environments.

Well, the files within the VM container file are not accessable
directly from the Win10 host, but the VM has access to a couple of
shared folders where the application are stored. Just the usual
"connect to remote folder" from WinXP to Win10...

Which likely involves using SMBv1, which no properly configured Win10
system will allow these days.

[Jan-Erik Söderholm]

Post by Craig A. Berry

Post by Jan-Erik Söderholm

Post by Jan-Erik Söderholm
I have Win10 64bit on my laptop. To be able to support and change
two old VB6 applications (the VB6 dev environment has some issues on
win10) I installed Virtual Box, created an instance, installed WinXP
(directly from the original CD to the new VM instance) and then
installed the VB6 IDE there. Worked just fine. All files are
accessable from both the WinXP and Win10 environments.

Well, the files within the VM container file are not accessable
directly from the Win10 host, but the VM has access to a couple of
shared folders where the application are stored. Just the usual
"connect to remote folder" from WinXP to Win10...

Which likely involves using SMBv1, which no properly configured Win10
system will allow these days.

I have absolutely no idea. How to check that? And what is a "properly
configured Win10 system"? I have done no special configuration apart
from the upgrade from Win7. Just "shared" the forldes from Win10 and
connected from WinXP.

[Stephen Hoffman]

Post by Jan-Erik Söderholm

Post by Craig A. Berry

Post by Jan-Erik Söderholm
Well, the files within the VM container file are not accessable
directly from the Win10 host, but the VM has access to a couple of
shared folders where the application are stored. Just the usual
"connect to remote folder" from WinXP to Win10...

Which likely involves using SMBv1, which no properly configured Win10
system will allow these days.

I have absolutely no idea. How to check that? And what is a "properly
configured Win10 system"? I have done no special configuration apart
from the upgrade from Win7. Just "shared" the forldes from Win10 and
connected from WinXP.

Microsoft has been trying to kill SMBv1 for a while now, as it's become
little more than a system compromise mimicking a file share.
Here's how to re-animate the corpse in Windows 10, for any folks that
need access to OpenVMS with the old Samba CIFS port, or to Windows XP...
https://social.technet.microsoft.com/Forums/en-US/9fd07a6b-62dc-40b0-995c-5a3a5d533150/how-to-enabledisable-smbv1-in-windows-10

[Arne Vajhøj]

Post by Dave Froble
A question, does anyone know if I can take an existing system and move
it to a VM?  I'm guessing I can "export" stuff to another system.  But I
might want to keep some older stuff without having to re-install everything.

Some VM software has some capabilities. Note that such capabilities
are often features in the for-pay versions and missing in the free
versions.

https://www.howtogeek.com/213145/how-to%C2%A0convert-a-physical-windows-or-linux-pc-to-a-virtual-machine/

has some examples.

Arne

[Chris Scheers]

Post by Dave Froble
Well, I downloaded Virtual Box V6.??, and tried to install it on a 32
bit Win XP box. No luck, it needs 64 bit WEENDOZE.
I had a V4.2.? I must have downloaded in the past. No longer supported,
but, I doubt it stopped working just because it's no longer supported.
Installed fine on the box.
Created a new VM. Then loaded 32 bit WEENDOZE 7 on it. That seems to
almost work Ok. I'm having a problem getting the VM instance to see
other computers on my network. Playing with it, I may have made things
worse. Oh, well, that's what learning is all about.

With VirtualBox, I usually use "bridged" mode for the emulated network
controller. This should put the VM on your local subnet.

One thing to watch out for is TOE settings on the host's physical
Ethernet controller. The most common symptom of this is that the host
and VM can not communicate, but other boxes on the network can talk to
the VM.

If you see this, you may need to disable TOE (TCP/IP Offload Engine)
settings on the Ethernet controller.

Good luck!

[Dave Froble]

Post by Chris Scheers

Post by Dave Froble
Well, I downloaded Virtual Box V6.??, and tried to install it on a 32
bit Win XP box. No luck, it needs 64 bit WEENDOZE.
I had a V4.2.? I must have downloaded in the past. No longer
supported, but, I doubt it stopped working just because it's no longer
supported. Installed fine on the box.
Created a new VM. Then loaded 32 bit WEENDOZE 7 on it. That seems to
almost work Ok. I'm having a problem getting the VM instance to see
other computers on my network. Playing with it, I may have made
things worse. Oh, well, that's what learning is all about.

With VirtualBox, I usually use "bridged" mode for the emulated network
controller. This should put the VM on your local subnet.

To be honest, i had no idea what any of these settings meant. IS there
anything about them in the V-box documentation, that I didn't read?

But, BINGO! Changed the mode, and all my stuff came up under networks.

Post by Chris Scheers
One thing to watch out for is TOE settings on the host's physical
Ethernet controller. The most common symptom of this is that the host
and VM can not communicate, but other boxes on the network can talk to
the VM.

Since I see the host in Networks, can I assume (hate when I do that) I
don't need to worry about this setting?

Post by Chris Scheers
If you see this, you may need to disable TOE (TCP/IP Offload Engine)
settings on the Ethernet controller.
Good luck!

Thanks ...

[Chris Scheers]

Post by Dave Froble

Post by Chris Scheers

Post by Dave Froble
Well, I downloaded Virtual Box V6.??, and tried to install it on a 32
bit Win XP box. No luck, it needs 64 bit WEENDOZE.
I had a V4.2.? I must have downloaded in the past. No longer
supported, but, I doubt it stopped working just because it's no longer
supported. Installed fine on the box.
Created a new VM. Then loaded 32 bit WEENDOZE 7 on it. That seems to
almost work Ok. I'm having a problem getting the VM instance to see
other computers on my network. Playing with it, I may have made
things worse. Oh, well, that's what learning is all about.

With VirtualBox, I usually use "bridged" mode for the emulated network
controller. This should put the VM on your local subnet.

To be honest, i had no idea what any of these settings meant. IS there
anything about them in the V-box documentation, that I didn't read?
But, BINGO! Changed the mode, and all my stuff came up under networks.

In the 4.2.18 User Manual, read chapter 6 carefully.

"bridged" mode makes the VM a member of your subnet, just as if a
physical box was connected. That also means that the VM can screw with
your subnet.

Post by Dave Froble

Post by Chris Scheers
One thing to watch out for is TOE settings on the host's physical
Ethernet controller. The most common symptom of this is that the host
and VM can not communicate, but other boxes on the network can talk to
the VM.

Since I see the host in Networks, can I assume (hate when I do that) I
don't need to worry about this setting?

If you can transfer data back and forth between the host and the VM, you
should be good.

I mentioned TOE settings because they can really mess up VM
communications and they are hard to diagnose. I see TOE causing
problems most often with Intel and Broadcom adapters.

Another "issue" that is starting to come up is ECN, especially with
older operating systems. I haven't noticed it (yet) with Windows, but I
have seen it with some other network stacks. (The definition of ECN is
not completely upwards compatible.)

Post by Dave Froble

Post by Chris Scheers
If you see this, you may need to disable TOE (TCP/IP Offload Engine)
settings on the Ethernet controller.
Good luck!

Thanks ...

[Arne Vajhøj]

Post by Phillip Helbig (undress to reply)

Post by g***@rlgsc.com
Traditionally, OpenVMS has been run on dedicated hardware.
With the advent of OpenVMS on x86, there is an increasing discussion of
running OpenVMS x86 on various virtual machine hypervisors

Since VMS will soon run natively on x86, what is the motivation to run
it on some sort of emulator?

Other have explained that hypervisor <> emulator.

That still leaves the why question.

Save money.

If you go to a vendor and ask for a small x86-64 server
you will get something like a 1 socket 16 core 32 threads
@ 3 GHz and 128 GB RAM thingy.

If you use that as a single server then most likely
HW utilization will be <5% maybe even <1%.

So you stuff 10-25 virtual servers into this single
physical box.

VMS are no different from Linux or Windows
in this regard.

So you buy one box and run 2 VMS instances,
1 big Linux instance with 10 containers,
5 other Linux instances and 5 Windows instances.

Or something like that.

Arne

[Dave Froble]

Post by Phillip Helbig (undress to reply)

Post by g***@rlgsc.com
Traditionally, OpenVMS has been run on dedicated hardware.
With the advent of OpenVMS on x86, there is an increasing discussion of
running OpenVMS x86 on various virtual machine hypervisors

Since VMS will soon run natively on x86, what is the motivation to run
it on some sort of emulator?

Well, as mentioned, it depends.

Don't confuse emulation with a VM. At least the way I understand
things, if VMS runs on x86 as a VM guest, it's not emulation.

For some there may be no reason to do so.

Now, what if the only HW supported is some rather high end stuff, and
expensive. A casual user, a developer, and such, could have a VMS
environment with less expensive HW and a VM.

Only got one system, but want 2 or more instances of VMS running?
Multiple guests in a VM.

Perhaps as many reasons as there are participants in c.o.v.

Since you're into running a cluster, whether or not you need one, how
about 2 systems, with one running a second guest to allow a 3 node
cluster? Though, that's a rather poor idea, since if you lose the
system with 2 guests, you lose quorum, at a minimum.

How about a hypothetical VM that provides a whole bunch of security?

[Scott Dorsey]

Post by Phillip Helbig (undress to reply)

Post by g***@rlgsc.com
Traditionally, OpenVMS has been run on dedicated hardware.
With the advent of OpenVMS on x86, there is an increasing discussion of
running OpenVMS x86 on various virtual machine hypervisors

Since VMS will soon run natively on x86, what is the motivation to run
it on some sort of emulator?

The ability to snapshot systems, to shut them down and restore them on
different hardware on the fly without users noticing. Zero downtime for
maintenance.
--scott

[David Wade]

Post by Phillip Helbig (undress to reply)

Post by g***@rlgsc.com
Traditionally, OpenVMS has been run on dedicated hardware.
With the advent of OpenVMS on x86, there is an increasing discussion of
running OpenVMS x86 on various virtual machine hypervisors

Since VMS will soon run natively on x86, what is the motivation to run
it on some sort of emulator?

Well whilst others have said "virtual" is not "emulation" I would say it
is emulation of sorts, but done at the microcode level in the chip.

As to why, well many reasons. I think for most industry the biggest
driver is a reduction in cost. Its not just the cost of the base
hardware. Servers need cooling and power and floor space all of which
are expensive. Virtualization allows you to run multiple copies of an OS
on one box. More than that most modern Hypervisors allow you to move the
running virtual image to a different server, while its running.

This means you can load balance and really optimize your farm to the
minimum hardware without compromising availability.

The second is that it decouples the software from the hardware. Virtual
Machines present virtual peripheral interfaces. When you upgrade the
hardware the OS still sees the same type of peripheral....

Dave

[Dave Froble]

Post by David Wade
The second is that it decouples the software from the hardware. Virtual
Machines present virtual peripheral interfaces. When you upgrade the
hardware the OS still sees the same type of peripheral....

This I think is a rather important point.

When people talked about VMs, I of course "knew everything", ever when I
knew nothing, and didn't want to trust running on top of WEENDOZE
garbage or Linux snake oil.

Well, even an old dog just may be able to learn some new tricks, we'll
see ....

As I was trying to learn Virtual Box, it occurred to me that perhaps I
could run old stuff on new HW. A big problem I've had in resisting
WEENDOZE 7, and beyond, was lack of drivers for newer HW.

So in time, I'm going to attempt to load stuff as far back as WEENDOZE
95, maybe even MS-DOS, on some VM instances. Now, where is that old
submarine game I used to enjoy ....

Might need a virtual floppy drive ....

[Simon Clubley]

Post by Dave Froble
So in time, I'm going to attempt to load stuff as far back as WEENDOZE
95, maybe even MS-DOS, on some VM instances. Now, where is that old
submarine game I used to enjoy ....

If you want to run MS-DOS applications, another alternative is DOSBox.

Works just fine for me under Linux.

https://www.dosbox.com/information.php?page=0

You can also run some Windows 95 applications directly under Linux
by using Wine. Success rate varies heavily by application however.

https://www.winehq.org/

Simon.

[t***@glaver.org]

Post by g***@rlgsc.com
Traditionally, OpenVMS has been run on dedicated hardware. In the past two decades, an initially small but increasing number of systems have been, and are, running on one or another emulator (e.g., simh, Charon, AVT, etc.). With the advent of OpenVMS on x86, there is an increasing discussion of running OpenVMS x86 on various virtual machine hypervisors (e.g., xen, VirtualBox, Hyper-V).
Questions ensue along the lines of "What if my (fill in your supported VM) infrastructure is using enterprise-class storage facility that is not supported by OpenVMS?"
What matters in a hypervisor-based environment is not the underlying storage or network device used by the hypervisor. What does matter is the simulated device presented to the client virtual machine.

I discovered this (with an emulator, not a hypervisor) when I found that the AlphaVM emulator could attach SAS and SATA drives directly to the emulated VMS instance. I expected SAS would work (the most common use seems to be directly connecting a physical tape drive to the emulated VMS system) but was rather surprised that SATA worked - apparently the SAT layer handles the command differences. This is slower than providing a virtual drive to the emulated VMS system, since the attached device no longer benefits from optimizations / caching performed by the host operating system. In the case of AlphaVM, it provides some assists (6/10 byte command conversion, SCSI ID and LUN translation, etc.)