VMware ESXi and vSphere Cluster Management
What Is a Virtual Disk in VMware Player?
Learn how VMware virtual disks work, where VMDK files are stored, how capacity is allocated, and how to safely move, attach, or remove virtual disks.
A virtual disk is file-based storage that a virtual machine uses like a physical hard drive. VMware Player presents this storage to the guest operating system as a disk device, even though the disk data is stored as one file or a related set of files on the host computer.
This distinction is important: a virtual disk is not an additional physical hard drive or SSD installed in the host. It is a software-defined storage device backed by space on an existing host filesystem.
Host, guest, and virtual machine
The host system is the physical computer and operating system that run VMware Player. The host filesystem organizes the folders and files used by the virtual machine.
A virtual machine is a software-defined computer with virtual hardware such as a processor, memory, network adapter, and disk. The guest operating system is the operating system running inside that virtual machine.
VMware Player connects the guest's virtual hardware to files on the host. For storage, a virtual disk file becomes visible inside the guest as a normal-looking disk device.
What a virtual disk does
The virtual disk normally contains the guest operating system, its applications, user files, partitions, filesystems, and other data. When a new virtual machine is created, it commonly starts with one virtual disk for the operating system.
From inside the guest, the disk can usually be managed with ordinary operating-system tools. The guest can:
- Partition the disk.
- Format a partition with a filesystem.
- Mount the filesystem and create files.
- Read, modify, and delete data.
For example, a Linux virtual machine created with a 60 GB virtual disk can present that disk to the installer. The installer can partition and format it just as it would a physical disk, while VMware stores the resulting disk data on the host.
How VMware virtual disk files are represented
VMware virtual disks commonly use the VMDK format, identified by the .vmdk filename extension. One logical virtual disk may be stored in one file or in several related files, depending on how the disk was created and configured.
A VM folder can contain several kinds of files. The VMDK file or file set holds virtual disk data. Other files hold the virtual machine's configuration or temporary memory state. These files have different purposes, so a file that belongs to the VM is not automatically a virtual disk.
Use the host file manager to locate the VM folder and identify filenames ending in .vmdk. Do not rename, separate, or manually edit virtual disk files while the virtual machine is running.
Conceptual VM folder layout
Example VM folder
├── VM configuration files
├── VM memory-state files, when present
├── system-disk.vmdk
└── related VMDK files, when the disk uses multiple filesThe exact filenames and number of files can vary. Treat all files belonging to one disk as a unit, especially when copying or moving it.
How the host and guest see capacity
Disk capacity is the maximum size of the virtual disk presented to the guest. A guest might see a disk with a capacity of 60 GB or 100 GB even when the host currently uses much less physical space for its VMDK data.
| Concept | What the guest sees | What exists on the host |
|---|---|---|
| Virtual disk | A disk device that can contain partitions and filesystems | One file or a related set of files representing storage |
| Physical disk | A disk device supplied directly by physical hardware | An actual hard drive or SSD installed in or attached to the computer |
| VMDK file or file set | Usually not seen directly as a host filename | VMware virtual disk data with a .vmdk extension |
| Configured capacity | The maximum disk size reported to the guest | A limit that may be larger than the space currently consumed on the host |
Host free space places a practical limit on the guest. Even if the guest has free capacity according to its disk layout, the host must still have enough space for VMware to store additional VMDK data and other VM files.
Dynamic and preallocated virtual disks
Virtual disks can use different allocation methods. The allocation method controls when host storage is reserved, not the maximum capacity that the guest can see.
Dynamically allocated disks
A dynamically allocated disk, also called a growable disk, starts by using relatively little host storage. Its host-side data grows as the guest writes more data, up to the configured maximum capacity.
For example, a disk with a 100 GB maximum might initially consume only a small amount of host space. Installing applications and saving guest files can cause the VMDK data to grow toward 100 GB.
Preallocated disks
A preallocated disk reserves its intended capacity on the host when it is created. A 100 GB preallocated disk therefore requires approximately that amount of host storage immediately, even if the guest has stored very little data.
| Allocation method | Initial host space used | Growth behavior | Main benefit | Main consideration |
|---|---|---|---|---|
| Dynamically allocated | Relatively small amount | Grows as guest data is written, up to the maximum | Uses less host space at the beginning | Host storage must be monitored because usage can increase unexpectedly |
| Preallocated | Approximately the configured capacity | Capacity is reserved at creation | Predictable host-space reservation and often faster creation-time planning | Requires substantial free space immediately and can make copying a large disk more demanding |
Both methods have portability implications. A smaller dynamic disk may initially be quicker to copy, but it can grow during use. A preallocated disk has a predictable size, but moving it requires enough destination storage for the reservation.
Managing virtual disks in VMware Player
Use the virtual machine's hardware or settings controls to inspect its existing hard disks and their attachments. These controls can be used to add another virtual disk, detach an existing disk, or review disk-related configuration.
Power off the virtual machine before making major virtual hardware or disk attachment changes when appropriate. Do not treat a running guest like a safe target for manually rearranging its disk files.
| Action | Purpose | Important precaution |
|---|---|---|
| Add a disk | Give the VM additional storage for data, projects, or another operating system | After attachment, initialize, partition, format, and mount the disk using guest operating-system tools |
| Remove or detach a disk | Remove the disk's association from the VM configuration | Confirm whether it is a secondary data disk or the boot/system disk, and decide whether to retain its VMDK files |
| Change disk settings | Review or adjust the virtual disk's hardware configuration through VM settings | Power off the VM when the change requires it and keep a recovery plan for important data |
| Move disk files | Store the disk in another folder, drive, or compatible computer | Move every associated disk file together and ensure the VM configuration points to the new path |
Removing a disk versus deleting its data
Removing or detaching a disk from the VM configuration changes the disk attachment: the VM no longer connects that virtual hardware to the disk. This action is different from deleting the underlying .vmdk file or file set.
Retain the disk files if you may need to reconnect the disk later. Delete them only when you have confirmed that the data is no longer needed and that no other VM configuration depends on them. Removing the boot disk can prevent the guest from starting.
Moving and using virtual disks on another computer
Virtual disk data is portable because it is stored in files on the host filesystem. You can move a disk to another folder on the same host or transfer it to another compatible computer.
- Power off the virtual machine.
- Identify the complete VMDK file or file set belonging to the disk.
- Copy or move the files without splitting apart related files.
- Ensure the destination has sufficient free storage.
- Open or update the VM configuration so its disk reference points to the new location.
- Check permissions and confirm that the transferred files are intact before starting the VM.
A moved disk may not work immediately if the VM configuration still references the old path. In that case, reconnect the disk through the VM's settings controls or restore the disk to the expected location. Compatibility between VMware versions and the destination environment can also matter.
Practical examples
Creating a new VM
A user creates a Linux VM with a 60 GB virtual disk. The Linux installer sees a disk suitable for partitioning and installation. The host stores the disk as VMware VMDK data inside the VM's folder.
Dynamic growth
A 100 GB dynamically allocated disk begins with a small host footprint. As the guest receives applications and project files, its VMDK data grows. The host must retain enough free space for that growth.
Adding storage
A VM runs out of room for project files, so the user attaches a second virtual disk. The guest detects a new disk device. The user then initializes it, creates a partition and filesystem, and mounts it for data storage.
Moving a VM disk
A user moves a VM folder to another drive or computer. The complete VMDK file set is copied intact, and the VM is opened with valid disk paths. The destination also needs appropriate permissions and sufficient storage.
Troubleshooting virtual disk problems
The host runs out of storage
A dynamically allocated disk may have expanded as the guest wrote more data. Free or add host storage, review the disk's maximum capacity, and monitor host free space before continuing. A guest's reported free space does not guarantee that the host can accommodate future growth.
The VM cannot find its disk after moving files
The VM configuration may still point to the previous path, or a multi-file disk may have been copied incompletely. Restore the complete disk file set, keep its members together, and reconnect or update the disk reference through the VM settings.
Deleting guest files did not reduce host usage
Deleting files releases space inside the guest filesystem, but the VMDK may keep its existing host allocation. Explain the difference between guest free space and physical host space consumed, and use supported disk-reclamation procedures only when host-space recovery is required.
The VM no longer boots after a disk was removed
The detached disk may have been the guest's boot or system disk, or it may contain data required during startup. Reattach the correct disk and verify disk roles before making further changes. Avoid removing a system disk without a recovery plan.
A copied VM reports permissions or access errors
Check whether the destination account can read and write the VM folder. Also check destination capacity and the integrity of the transferred disk files. Permission problems and incomplete transfers can both prevent VMware from opening or using a VMDK.
Key points to remember
- A virtual disk is file-based storage presented to the guest as a normal disk device.
- VMware virtual disks commonly use the
.vmdkextension and may consist of one file or multiple related files. - The guest's configured capacity can be larger than the host space currently consumed.
- Dynamic disks grow with guest writes; preallocated disks reserve their capacity at creation.
- Host free space ultimately limits how much data the guest can write.
- Detaching a disk from a VM is not the same as deleting its VMDK data.
- When moving a disk, keep all associated files together and update the VM's disk path if necessary.
- Power off the VM before major disk or virtual hardware changes whenever appropriate.
For the related concept of virtual disk storage, continue with What Is a Virtual Disk?