Hello, We develop a sandboxed Mac App Store app that runs virtual machines with Virtualization.framework on Apple silicon (macOS 27). Users want to install a macOS guest onto an external USB disk and start the VM from it, so they can keep a VM on portable storage or on a disk larger than the Mac's internal drive. What we tried USB passthrough: we attach the disk before the VM starts, with VZUSBPassthroughDeviceConfiguration (from an AAUSBAccessory) on a VZXHCIControllerConfiguration. Linux guests install onto the disk and boot from it without problems. For a macOS guest, VZMacOSInstaller fails to start when the USB disk is the only storage: As we understand it, a macOS VM can only start from its own storage devices, never from a USB device, so even a successful install would not boot. VZDiskBlockDeviceStorageDeviceAttachment: this needs an open file handle to /dev/diskN. That requires admin rights, which a sandboxed app can't obtain, so we can't use it in our App Store app. Questions Is there a supported way to install a macOS guest onto an external USB disk and start the VM from it? Is there a sandbox-compatible way to get a VZDiskBlockDeviceStorageDeviceAttachment for an external disk, for example after user consent, similar to how AccessoryAccess grants USB devices? If neither is possible today, is support for this planned, or is there a recommended alternative? Thank you for any guidance.

Installing a macOS guest onto an external USB disk with Virtualization.framework (sandboxed app)

Hello,

We develop a sandboxed Mac App Store app that runs virtual machines with Virtualization.framework on Apple silicon (macOS 27). Users want to
install a macOS guest onto an external USB disk and start the VM from it, so they can keep a VM on portable storage or on a disk larger than the
Mac's internal drive.

What we tried

USB passthrough: we attach the disk before the VM starts, with VZUSBPassthroughDeviceConfiguration (from an AAUSBAccessory) on a
VZXHCIControllerConfiguration.
- Linux guests install onto the disk and boot from it without problems.
- For a macOS guest, VZMacOSInstaller fails to start when the USB disk is the only storage:
- As we understand it, a macOS VM can only start from its own storage devices, never from a USB device, so even a successful install would not
  boot.
VZDiskBlockDeviceStorageDeviceAttachment: this needs an open file handle to /dev/diskN. That requires admin rights, which a sandboxed app can't
obtain, so we can't use it in our App Store app.

Questions

Is there a supported way to install a macOS guest onto an external USB disk and start the VM from it?
Is there a sandbox-compatible way to get a VZDiskBlockDeviceStorageDeviceAttachment for an external disk, for example after user consent,
similar to how AccessoryAccess grants USB devices?
If neither is possible today, is support for this planned, or is there a recommended alternative?

Thank you for any guidance.