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Recently I've been wondering about minimal OS X VMs on Mac Pro-hosted ESXi instances. How small can one go...?
Well, macOS doesn't really have install options anymore (unlike the Classic Mac OS days), so there's no way to do a minimal install. There's just the default install, and it'd be really tricky to know what is safe to trim down from that. Probably better off to leave it as-is.

Most hypervisors can support sparse disk images, so that would be your primary way of not using more disk space than you have to. An install of macOS Mojave would take about 12 GB. macOS doesn't bloat up the way Windows does (due to Windows SxS), so your disk usage after that would be dependent on what you install and add to it.
 


Ric Ford

MacInTouch
Well, macOS doesn't really have install options anymore (unlike the Classic Mac OS days), so there's no way to do a minimal install. There's just the default install, and it'd be really tricky to know what is safe to trim down from that.
True, although there's an interesting, extremely minimal system in the invisible Recovery HD partition. I found a way to take a look at it, but this is not recommended and may have adverse effects - attempt at your own risk....
Bash:
sudo mkdir /Volumes/RecoveryHD
diskutil list

/dev/disk2 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *2.0 TB     disk2
   1:                        EFI EFI                     209.7 MB   disk2s1
   2:                  Apple_HFS Log12_SanDisk           11.5 GB    disk2s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk2s3

sudo mount -t hfs /dev/disk2s3 /Volumes/RecoveryHD
 


Recently I've been wondering about minimal OS X VMs on Mac Pro-hosted ESXi instances. How small can one go...?
There is utility called TechTool Pro that enables you to create a bootable drive with a minimal system install and the TechTool Pro application that you can use to boot your computer and fix issues. The minimal install takes 2.78 GB. You can customize it right up to a full OS X install.
 


There is utility called TechTool Pro that enables you to create a bootable drive with a minimal system install and the TechTool Pro application that you can use to boot your computer and fix issues. The minimal install takes 2.78 GB. You can customize it right up to a full OS X install.
I'm guessing this approach is (or once was) documented somewhere, since a few commercial products have done this. Alsoft's DiskWarrior was another, for example.
 


Bad news, everyone - I couldn't get this to work. There are many old references on the Internet to converting a .dmg to .vmdk using VMWare Fusion's rawdiskCreator and vdiskmanager utilities (e.g. this one). There are also many references to "p2v" (physical-to-virtual), all of which are great for Windows but ultimately no good for macOS.
One final note on all this virtualisation testing, something I thought of this morning and tried: As you can very easily create an OS X 10.11 or macOS 10.12 virtual machine with VMware Fusion, and they offer a 30-day trial, I wondered if you could easily create the virtual machine in Fusion first and then somehow import/use it with VirtualBox. Low and behold, you can! I've outlined the steps how to do this in my articles on MacStrategy.

Obviously, as I've commented here before, VirtualBox is not for the faint-hearted. I still recommend purchasing Parallels Desktop or VMware Fusion - they are simply better, more polished products all around. But if you want to use the free VirtualBox and want to get an OS X 10.11/macOS 10.12 virtual machine going, it appears you can (with a little help from Fusion).
 


Bad news, everyone - I couldn't get this to work. There are many old references on the Internet to converting a .dmg to .vmdk using VMWare Fusion's rawdiskCreator and vdiskmanager utilities (e.g. this one). There are also many references to "p2v" (physical-to-virtual), all of which are great for Windows but ultimately no good for macOS.
I created my .dmg's from working OS X 10.8 and macOS 10.12 hard disk partitions then tried to use the above instructions (or the myriad of similar ones on the internet). None of them would work. The second, vdiskmanager, command would generally fail with a "Received signal 11" error message. Googling this turned up this bug in Fusion 11. I can only assume the bug is still there in v12.

After what many viewed as, Apple's deliberate requirement of crippling VM software to not be able to use the client version of Mac OS X 10.6, I wouldn't put it past Apple that this bug has been deliberately required/introduced to stop users converting a .dmg to .vmdk.

In our use case, this feature would be really useful, but, of course, its primary use would end up being for Windows/Linux users to easily take a pre-installed .dmg of an OS X/macOS installation and convert and run it on non-Apple hardware, which would totally bypass the need for Apple hardware and the requirement to download and use the OS X/macOS installer to set up a virtual environment in the first place. Apple will no doubt take all action necessary to cripple a "feature" that allowed this to happen… (YDVOAMV - Your Dystopian View Of Apple May Vary).

On the good news side, what I could get to work is to create a clean OS X/macOS virtual environment (but not in VirtualBox) and then use Apple's Migration Assistant on first boot to access and use a .dmg clone to copy across the original setup/installation, users, applications and files. Of course, this requires setting up the basic/clean VM in the first place, on Apple hardware with Apple's official OS X/macOS installer, but at least this is possible.
With Mac OS X 10.6, you must have the Server version to make into a Fusion virtual drive. From OS X 10.8 and above, you can use the client OS to create virtual drives.

I like to create initial clean installs and then save them as stock virtuals. I can then duplicate them and install any additional apps, updates and drivers and know that I have a good clean start to work from. Also, as you noted above, you can migrate from any clone or Time Machine backup to that virtual drive. This will become more important as Apple transitions to an all-64-bit OS and the ongoing issues that older apps have with the new APFS file system.
 


With Mac OS X 10.6, you must have the Server version to make into a Fusion virtual drive. From OS X 10.8 and above, you can use the client OS to create virtual drives.
I like to create initial clean installs and then save them as stock virtuals. I can then duplicate them and install any additional apps, updates and drivers and know that I have a good clean start to work from. Also, as you noted above, you can migrate from any clone or Time Machine backup to that virtual drive. This will become more important as Apple transitions to an all-64-bit OS and the ongoing issues that older apps have with the new APFS file system.
Thank you for your input, but I think you've missed all our previous postings and conversation, so to summarise for everyone: we already know all about Mac OS X 10.6 needing to be the Server version. This has been extensively discussed here in the past, and I put together a step-by-step guide for virtualising this version of Mac OS X over on MacStrategy:

We've been discussing the need to run 32-bit applications in the future (macOS 10.15 onwards) and I maintain a list here:

I wanted to put together step-by-step guides for virtualising OS X 10.8, OS X 10.11 and macOS 10.12 - I didn't bother with other OS versions for various reasons already stated on MacInTouch:

A lot of this testing was done primarily to get Adobe Creative Suite running. I have documented my testing and findings:

All of this has raised a few points:
• VirtualBox is free but has many quirks and is not easy to use, unlike Parallels Desktop and VMware Fusion, which are very easy to use. It was okay to get OS X 10.8 virtualised with VirtualBox, but later versions of macOS just did not work.​
• This led to that fact that you can actually use a trial version of VMware Fusion to easily virtualise later versions of macOS and then transfer/import the virtual hard disk to VirtualBox​
• This also led to the question of whether you could take an existing macOS installation and "convert" it for use in a virtual environment.​
• This led to the fact that virtualising macOS generally requires starting from scratch, requiring an official Apple installer and setting up the virtual machine on Mac hardware in the first instance.
• Which proved that you cannot take a disk image .dmg clone of an existing macOS installation and "convert" it for use in a virtual environment.​
• But it did lead to the fact that you can use a Time Machine backup or clone of an existing macOS installation and "migrate" from it into an existing (clean) virtualised macOS environment.​
 


Which proved that you cannot take a disk image .dmg clone of an existing macOS installation and "convert" it for use in a virtual environment.
Have you tried a procedure like this (for VMware Fusion)?

To summarize the procedure: take a dmg clone like you have, mount it within an existing macOS VM. Attach and mount a new, empty vmdk to the VM, and use CCC or similar to copy the mounted dmg volume to the vmdk-backed volume. Use Startup Disk to select the new vmdk volume as the startup disk. Shutdown the VM, and remove the original vmdk. Fingers crossed, the VM boots successfully from the new vmdk, which is cloned from your physical machine.
 


Have you tried a procedure like this (for VMware Fusion)?

To summarize the procedure: take a dmg clone like you have, mount it within an existing macOS VM. Attach and mount a new, empty vmdk to the VM, and use CCC or similar to copy the mounted dmg volume to the vmdk-backed volume. Use Startup Disk to select the new vmdk volume as the startup disk. Shutdown the VM, and remove the original vmdk. Fingers crossed, the VM boots successfully from the new vmdk, which is cloned from your physical machine.
Thanks - a very interesting approach which I haven't tried yet. I will try to set aside some time to test this method this week/next week.
 


Thanks - a very interesting approach which I haven't tried yet. I will try to set aside some time to test this method this week/next week.
I just realised my test rig's VMware Fusion trial runs out tomorrow, so I moved my work schedule around and did some testing today.

Yippee - success!!

I've been able to clone across from disk image files of various operating systems using VMware Fusion. I've documented the steps over on MacStrategy:

Many thanks to Todd Bangerter for pointing us in the right direction.
 



I just realised my test rig's VMware Fusion trial runs out tomorrow, so I moved my work schedule around and did some testing today.
Yippee - success!!
I've been able to clone across from disk image files of various operating systems using VMware Fusion. I've documented the steps over on MacStrategy:
Many thanks to Todd Bangerter for pointing us in the right direction.
It seems like you should be able to do this directly from macOS, rather than inside a virtual machine.

VMware Fusion has the ability to directly read a host drive, a.k.a. "raw disk". It does this by creating a metadata .VMDK file that links to the actual drive.

So, per VMware, all you have to do is use vmware-rawdiskCreator to create the .VMDK linked to a host drive, then use vmware-vdiskmanager to create a normal file-based .VMDK by copying from the metadata .VMDK.

Both tools are found in /Applications/VMware Fusion.app/Contents/Library.

I said "per VMware" because they did say this is the right procedure, but they did not list the precise command syntax needed. So, 10 points to whoever can find the best link to a website that actually says how to do this.
 


It seems like you should be able to do this directly from macOS, rather than inside a virtual machine.

VMware Fusion has the ability to directly read a host drive, a.k.a. "raw disk". It does this by creating a metadata .VMDK file that links to the actual drive.

So, per VMware, all you have to do is use vmware-rawdiskCreator to create the .VMDK linked to a host drive, then use vmware-vdiskmanager to create a normal file-based .VMDK by copying from the metadata .VMDK.

Both tools are found in /Applications/VMware Fusion.app/Contents/Library.

I said "per VMware" because they did say this is the right procedure, but they did not list the precise command syntax needed. So, 10 points to whoever can find the best link to a website that actually says how to do this.
I've been there and tried that - it doesn't work! It works for PC Windows environments but it doesn't work for macOS.

It used to (maybe) work - there are many, many step-by-step guides on the internet to do this for macOS but they are all at least three years old (BTW, I've tried them all and spent hours testing them a couple of weeks ago). This feature stopped working for macOS environments with Fusion 10 (apparently due to a bug in vmware-vdiskmanager when working with macOS disks). That bug has never got fixed.

My personal speculation is that it is a deliberate bug (probably required by Apple) to specifically block this feature, because it allows Windows/Linux users to simply download a .dmg of a macOS installation, convert it and virtualise it on their non-Apple hardware without the need for a Mac, Apple ID, the App Store or an original macOS installer.

The methods we have managed to get working all require a real Mac and/or original macOS installer - so for Apple, those methods are all fine/allowable.
 


My personal speculation is that it is a deliberate bug (probably required by Apple) to specifically block this feature, because it allows Windows/Linux users to simply download a .dmg of a macOS installation, convert it and virtualise it on their non-Apple hardware without the need for a Mac, Apple ID, the App Store or an original macOS installer.
The methods we have managed to get working all require a real Mac and/or original macOS installer - so for Apple, those methods are all fine/allowable.
As far as I know, whether macOS can be virtualized on non-macOS hosts depends on whether the virtual machine's virtual SMC presents the key

ourhardworkbythesewordsguardedpleasedontsteal(c)AppleComputerInc

when probed by the Dont Steal Mac OS X.kext kernel extension.

Fusion on macOS does (for certain macOS versions only?), but VMware Workstation on Windows does not.

Hackintoshes get around this by using their own EFI boot loader.
 


Probably the worst issue using a virtual machine is that backups on the OSX side see opening Windows in the vm as a huge file that got changed. Hence, backups can take a while after visiting Windows. (Note that Carbon Copy Cloner just replaces the old 'C' drive file with a new one, even if the 'C is 100 gig or larger.)
I have had to struggle a bit to ensure I get good backups of my virtual machines. One practice that makes this manageable is that I shut down the virtual machines at the end of the day. As a start, I have excluded the virtual machine folder from the Time Machine backup. Then, I use a scheduled Chronosync script to back up the virtual machine folder to (several) other locations every few nights. I get my VM backups, and they are not hogging all of the space on my Time Capsule drive, as they're not backed up each hour. I mainly use Time Machine for the immediate hourly backups. I use Chronosync to do a bootable backup to another SSD every few days, so I don't have too much downtime if something stops my machine from booting.
 


I have had to struggle a bit to ensure I get good backups of my virtual machines. One practice that makes this manageable is that I shut down the virtual machines at the end of the day. As a start, I have excluded the virtual machine folder from the Time Machine backup. Then, I use a scheduled Chronosync script to back up the virtual machine folder to (several) other locations every few nights. I get my VM backups, and they are not hogging all of the space on my Time Capsule drive, as they're not backed up each hour. I mainly use Time Machine for the immediate hourly backups. I use Chronosync to do a bootable backup to another SSD every few days, so I don't have too much downtime if something stops my machine from booting.
Since all of my application data resides on the host machine volumes, it is backed up by Time Machine and by my regular Clone (CCC) backups. I also shut down all VMs and use CCC to copy them to a dedicated partition on my CCC target drives. This is done before updating Parallels or any other significant updates and as part of a monthly off-site backup process.

Recovery of a VM instance has become a simple Finder copy process. This is occasionally necessary because of Windows failures, Parallels VM corruption, Apple's changes, or, of course, user errors.
 


I've been there and tried that - it doesn't work! It works for PC Windows environments but it doesn't work for macOS.
You'll be pleased to know there is a fix coming for vmware-vdiskmanager (and thus Joe Chilcote's vfuse) throwing a "Received signal 11" error.
mikeroySoft said:
Error: Received Signal 11
Just FYI, but we are planning to ship a fix for this in the next few weeks. We wanted to get it in 11.0.3 but that release was specifically to address security vulnerabilities disclosed to us. I regret that we weren't able to bundle this fix with the .0.3 release, but please be assured it's coming =)
 


Does VMware Workstation Pro do a better job with hardware acceleration when run on Linux or Windows? Are these restrictions put in place by Apple based on the hardware or OS?
VMware Workstation does not support macOS as a guest (due to Apple's licensing restrictions).

The graphics acceleration issue with macOS guests is due to restrictions or lack of functionality in macOS by Apple (can't find the exact citation right now). No macOS guest on any virtualization platform will provide graphics acceleration. They can only do an emulated basic display driver.
So, on a Mac with a VM, is Final Cut Pro X completely unusable?
Final Cut Pro X will not launch.
Has anyone tried Logic X in a VM? I wonder how that would do.
I don't use Logic Pro X, but from what I've read, it does work.
 


BTW, Parallels has a tool to expand the Windows C [virtual] drive without erasing the drive.
VMware Fusion can also do this. I just did it the other day.
Probably the worst issue using a virtual machine is that backups on the OSX side see opening Windows in the vm as a huge file that got changed. Hence, backups can take a while after visiting Windows. (Note that Carbon Copy Cloner just replaces the old 'C' drive file with a new one, even if the 'C is 100 gig or larger.)
VMWare can use split virtual disks, where it's made up of a number of slices or fragments (kind of like DMG sparse bundles). Then, your backup program only has to backup slices that have had changes within them, so the amount you have to backup may be much less than the full disk size.
 


You'll be pleased to know there is a fix coming for vmware-vdiskmanager (and thus Joe Chilcote's vfuse) throwing a "Received signal 11" error.
Thanks for that. If and when they fix it, I will retest trying to directly bring a macOS disk image into a VM and post back here (and update my articles on MacStrategy).
 


VMware Workstation does not support macOS as a guest (due to Apple's licensing restrictions).

The graphics acceleration issue with macOS guests is due to restrictions or lack of functionality in macOS by Apple (can't find the exact citation right now). No macOS guest on any virtualization platform will provide graphics acceleration. They can only do an emulated basic display driver.

Final Cut Pro X will not launch.

I don't use Logic Pro X, but from what I've read, it does work.
Thanks Todd, very useful. Good to hear about Logic Pro X.

Which host OS are you referring to that "VMware Workstation does not support macOS as a guest"? I ask because in a different thread talking about VMware Workstation within Linux, it sounded like DFG and JohnW had some success running Sierra, El Cap and Snow Leopard VMs in Workstation.
 


Which host OS are you referring to that "VMware Workstation does not support macOS as a guest"? I ask because in a different thread talking about VMware Workstation within Linux, it sounded like DFG and JohnW had some success running Sierra, El Cap and Snow Leopard VMs in Workstation.
Officially "Workstation" doesn't support macOS as a guest. "Fusion" does. You can check the VMware product vs guest OS compatibility here:
 


Officially "Workstation" doesn't support macOS as a guest. "Fusion" does. You can check the VMware product vs guest OS compatibility here:
Thanks to Ric, I found out that the last paragraph of my original linked post had the answer:
As a FYI... Workstation can't install the macOS out of the box. You'll have to 'unlock' Apple-compatible VMs. Further information can be found by searching for "Unlocker for VMware Workstation." And finally there are a few tweaks that need to be added to the vmx file before you power on the VM for the first time.
So, with a workaround, it's doable.
 




Probably no different than what Steve_M mentioned doing here.
Aside from not having to emulate a PowerPC chip to run Mac OS 9, I suspect the use of the CPU/GPU passthrough tricks are a little different, though I haven't done anything with QEMU in years, and when I did, it was on a MIPS CPU. :)

Maybe Steve_M can comment.
 


While not for the faint of hackintosh heart or the timid in technical spirit, and some may find the host to be annoying, here is a video that describes an intriguing approach to creating a macOS virtual machine with potentially very high performance that should run on a very wide range of PC hardware
Aside from not having to emulate a PowerPC chip to run Mac OS 9, I suspect the use of the CPU/GPU passthrough tricks are a little different, though I haven't done anything with QEMU in years, and when I did, it was on a MIPS CPU. :)
Maybe Steve_M can comment.
I looked at the YouTube video, and it is seems fairly 'hard-core' from my perspective. Its appeal seems to be for users who want macOS on powerful/expandable/up-to-date hardware.
  • My Linux Mint machine is a MacBook Pro 6,2, and I am using Intel graphics, not the nVidia GPU
  • I am only running Mac OS 9.2 for occasional use and a bit of fun. I am happy with the performance, except for some problems with cursor synching.
  • I am not using KVM, but I might look into it now. I presently work with my QEMU PowerPC emulator via a VNC client on Linux. (The iMac/macOS Sierra QEMU binary I use provides a built-in GUI.)
  • I am not interested in running High Sierra or later - that is why I have taken up Linux. Sad, after starting with a Mac Plus in 1988.
So, in summary it is quite different from what I am doing!
 


I've been there and tried that - it doesn't work!
It works for PC Windows environments but it doesn't work for macOS.
[FYI:]
VMware said:
VMware Fusion 11.1.0 Release Notes
  • Virtual Disk Manager utility (vmware-vdiskmanager) to convert disk fails.
    When you use the Virtual Disk Manager utility (vmware-vdiskmanager) to perform a virtual disk conversion, the command fails and returns the following message: Received signal 11.

    This issue is fixed in this release.

    Note: Fusion needs to be launched in order for vmware-vdiskmanager to work. You can learn more details in the VMware Knowledge Base article https://kb.vmware.com/s/article/65163.
 



Thanks. I saw the new version had been released. I've added new testing to my to-do list but probably won't be able to get to it until next week.
I managed to reschedule and move stuff around, so I did some testing this afternoon. Unfortunately, it still doesn't work, but the problem is different.

The issue around using the Virtual Disk Manager utility (vmware-vdiskmanager) to convert disks on macOS has indeed been fixed - no more error "Signal 11". Virtual disk links can be created to physical drives/partitions, and Virtual Disk Manager now converts those drives/partitions to VM drives. The problem is that they are not bootable within Fusion.

The basic process is:
  1. Use vmware-rawdiskCreator to create a link to the drive/partition where macOS is installed.
  2. Use vmware-vdiskmanager to convert the drive/partition to a Fusion VM disk image.
  3. Attach the Fusion VM disk image to a new macOS VM in Fusion using Fusion's default settings for the relevant version of macOS that was on the original drive/partition.
  4. Adjust the VM settings as required e.g. increase the RAM to 4GB or 8GB.
  5. Boot the VM - this is it where it fails: you get the Apple logo, but during the boot process it fails - non-bootable circle with line through it icon.
I tried multiple different drives, partitions, macOS versions (10.8, 10.10, 10.11, 10.12), conversion processes, VM settings - and they all resulted in the same non-bootable OS error. It would be very nice if it worked, but, personally, I think this is just never going to work - it's not what Apple intended when they allowed virtualisation of macOS.
 


I updated my 2019 MacBook Pro to macOS 10.14.6 (18G87) this morning, and it has crashed twice since. Does anyone know if there's a problem with this release?
 


Parallels 15 has been released:

Interestingly, according to the What's New In Parallels 15 guide [PDF], graphics in Parallels Desktop 15 have been significantly improved, compared to previous product versions.
• With the help of Apple Metal, Parallels introduces support for DirectX 11. Now you can​
run Autodesk 3ds Max 2020, Lumion, ArcGIS Pro 2.3, products from MasterSeries and​
more. You can also play many favorite games, including Madden NFL 19, Age of​
Empires: Definitive Edition, Anno 2205, Railway Empire, Space Engineers, Frostpunk,​
Risk of Rain 2 and many more.​
• DirectX 3D graphics are now accelerated by the Apple Metal engine.​
• Enhanced compatibility with new Linux distributions due to Virtio GPU that supports​
sliding mouse (when Parallels Desktop captures the guest OS mouse cursor), dynamic​
resolution (when the screen resolution changes dynamically if you resize the virtual​
machine window) and multimonitor support—even without Parallels Tools.​
• Support for DRM-based graphics required by recent versions of major Linux​
distributions.​
Although not specifically mentioned, hopefully this might help with running graphics-intensive Apple apps in a virtual machine e.g. Aperture.
 


Ric Ford

MacInTouch
Interestingly, according to the What's New In Parallels 15 guide [PDF], graphics in Parallels Desktop 15 have been significantly improved, compared to previous product versions.
Although not specifically mentioned, hopefully this might help with running graphics-intensive Apple apps in a virtual machine e.g. Aperture.
Please let us know what you find if you do some testing of the new version. (Do you have Aperture available for testing?)
 


Please let us know what you find if you do some testing of the new version. (Do you have Aperture available for testing?)
When I get a chance (might not be for a couple of weeks), I will definitely do some basic Creative Suite i.e. Photoshop testing. I can't test Aperture, sorry, as I was never an Aperture user and don't have a licence for it.
 


When I get a chance (might not be for a couple of weeks), I will definitely do some basic Creative Suite i.e. Photoshop testing. I can't test Aperture, sorry, as I was never an Aperture user and don't have a licence for it.
I'll see about installing Aperture in Parallels 15 in the next few days.

Worth mentioning: I use (and like) both Parallels and VMware Fusion. One area of distinction between the two is that the current version of Parallels Desktop runs on a greater range of Apple hardware than does VMware Fusion.
  • VMware Fusion requires a Mac introduced in 2011 or later, with the exception of the 2012 Mac Pro Quad Core with the Xeon W3565, which is incompatible. Fusion also will run on 2010 Mac Pro 6-, 8-, and 12-core models.
  • In contrast, Parallels will run on just about any Mac with a Core 2 Duo processor or better. For example, I installed Parallels 15 on a 2010 Core 2 Duo MacBook Pro, and it is running a Windows 7 virtual machine very nicely.
 


Please let us know what you find if you do some testing of the new version. (Do you have Aperture available for testing?)
I finally got around to installing Aperture 3.6 on Parallels 15 virtual machines running High Sierra and Mojave. I also tried it on a VMware Fusion instance of a Mojave virtual machine.

Unfortunately, while Aperture is able to launch and run in those environments, it runs into the same display issue seen with previous virtualization solutions: image thumbnails are visible, but the main image viewing/editing pane is empty, so you can't actually see your images.

At the moment, it looks like the only real solution for running Aperture 3.6 is running it outside of a virtual machine.
 



I've copied VM files around, and they are big. I've always presumed they're somewhat analogous to applications on Mac that are packages which present as folders. Maybe someone else with real knowledge can clarify.
The specifics are going to vary based on what VM software you're running, but in general they contain a data file describing the VM's configuration (number of CPU cores, memory, networking, peripherals, etc.) and one or more disk images representing storage devices (typically hard drives).

On my Mac, running VirtualBox, the VM's configuration file is 7-9 KB. The disk image size depends on the size you specified when you created it and how it is configured. For instance, if you create a VM with a 60 GB storage device, that file could be up to 60 GB (a "dynamic" image will start small and grow up to its maximum size as you write data to it. A fixed-size image will always be the maximum size)

Other VM systems are probably going to be similar, possibly combining the files into a single "package" folder for easier management.
 


Links dense with information — I skimmed through, then turned to "find on this page", looking for, and not finding, any declaration that VMs are compressed internally. Thanks to Ric's links and subsequent posts by John W and David Charlap, it seems we can conclude with some certainty that WStein's SSD problem wasn't caused the nature of a VM.

While I've copied VMs around to backup disks, I've never tried to mount them back. The VirtualBox links suggested the kind of drag and drop copy I've done probably wouldn't work, because each VM has a unique UUID. (Without getting deep into that again, it's the same problem I had trying to mount a Clonzilla duplicate of a Linux drive on the machine containing the Clonezilla source.)...
 


I've copied VM files around, and they are big. I've always presumed they're somewhat analogous to applications on Mac that are packages which present as folders. Maybe someone else with real knowledge can clarify.
That's basically correct. You can right-click on Parallels and VMware VM files to show the package contents. I haven't done it in a while, but if I recall correctly, you can set the actual drive files within the packages to be single files or segmented files of arbitrary size in VMware and Parallels. If I recall correctly, early virtualization tools created drive files as 2GB segments by default. Some of my older VMs are formatted this way.
 


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