In the world of virtualization, small oversights can lead to major headaches. One such seemingly minor detail is forgetting to eject removable media—virtual ISOs, USB drives, and even virtual floppy disks—from VMware virtual machines (VMs). While this may sound trivial, it can cause serious operational problems, ranging from performance degradation and VM lockups to unexpected reboots and migration failures.
1. VMotion and Storage vMotion Failures
VMware vSphere allows for live migration of VMs using VMotion (for compute changes) and Storage vMotion (for disk changes). However, if a VM has an ISO mounted from a local datastore or client machine, migration will fail with an error like:
"The virtual machine requires access to a device that is only available on the current host."
This means that the VM is now effectively host-locked, preventing high availability (HA) or disaster recovery (DR) operations from working as expected.
2. VM Snapshots Becoming Bloated
If a VM has a virtual DVD drive mounted with an ISO or an external USB drive attached, and you take a snapshot, the snapshot may include references to these devices. This can lead to:
Larger snapshot files consuming unnecessary storage.
Restoration issues if the ISO or USB is missing when rolling back.
Performance degradation when running from a snapshot state.
3. Unexpected VM Boot Failures
Some VMs are configured to boot from CD/DVD or removable media as their first boot device. If an outdated or invalid ISO is still mounted, the VM may:
This is particularly dangerous in production environments where a reboot could happen unexpectedly due to patching or power failure.
4. USB Devices Causing Resource Contention
When a USB device is connected to a VM using USB passthrough, it is effectively removed from the ESXi host and dedicated to that VM. If the USB is not ejected:
Other VMs cannot access the device.
The host may experience resource contention if multiple VMs try to claim it.
If the VM is restarted, the device may fail to reconnect properly, requiring manual intervention.
5. Stale ISO References Blocking VM Operations
If a VM has a CD/DVD drive mapped to an ISO stored on a disconnected datastore, certain operations—like power on, reconfiguration, or migration—may fail with errors such as:
"Device 'CD/DVD drive 1' is backing a datastore that no longer exists."
This leads to administrative overhead, requiring manual removal of the stale device before operations can proceed.
Always Eject ISOs After Installation or Maintenance
In vSphere, navigate to the VM settings and set the CD/DVD drive to “Client Device” or “Host Device” instead of a specific ISO.
Use the vSphere Web Client or PowerCLI to ensure no unnecessary ISOs are attached.
Remove USB Devices When No Longer Needed
Detach USB devices properly via the VMware Remote Console or vSphere Client.
Avoid using USB passthrough unless absolutely necessary—prefer network-based solutions (e.g., file shares).
Automate Checks with PowerCLI
Run a periodic script to check for mounted ISOs across all VMs:
Get-VM | Get-CDDrive | Where-Object { $_.IsoPath -ne $null } | Select VMName, IsoPath
This helps ensure no VM is unknowingly holding onto an ISO.
Verify Boot Order in BIOS Settings
Audit and Remove Stale Device References
Wrap
Forgetting to eject removable media in VMware might not seem like a big deal—until it breaks your VM migration, slows down performance, or prevents booting when you need it most. By following best practices and automating checks, you can avoid unnecessary outages and reduce troubleshooting time.
So next time you finish installing software or transferring files on a VM, do yourself a favour—eject that ISO! 🚀
