VMware ESXi and vSphere Cluster Management
Understanding Virtual Disks in VMware Workstation Player
Learn how VMware virtual disks and VMDK files work, including capacity, growable and preallocated storage, disk management, relocation, and safe backups.
A virtual disk is a software-defined storage device attached to a virtual machine. VMware Workstation Player stores that disk as files on the host system: the physical computer and operating system running VMware. The guest operating system inside the virtual machine sees the virtual disk as a normal disk drive.
This difference between the guest view and the host view is the foundation of virtual-machine storage. The guest can partition and format the disk, install an operating system, install applications, and save documents without directly managing the host's folders.
Virtual disk concepts: guest view and host view
What a virtual disk contains
The virtual disk can contain nearly all of the guest's persistent storage, including:
- Guest operating-system files and boot information.
- Installed applications and their support files.
- User documents, downloads, projects, and media.
- Filesystem metadata, such as directory information, allocation records, permissions, and journaling data.
Deleting a file inside the guest usually marks its space as available to the guest filesystem. It does not necessarily make the corresponding host VMDK files immediately smaller. The virtual disk may retain that allocated space so it can be reused for later guest writes.
VMDK files and logical virtual disks
VMDK is VMware's virtual disk format. A VMDK is commonly identified by the .vmdk filename extension.
One logical virtual disk can be represented by one host file or by multiple related files. At a conceptual level, a multi-file disk may include:
- A disk descriptor, which contains metadata describing the virtual disk and how its data is organized.
- One or more extents, which hold the disk's stored data. An extent can be a data file or a portion of the logical disk's storage.
Users generally should not manually edit a descriptor or rearrange extent files. When copying, moving, or backing up a VMDK, preserve every associated component, its filename, and its directory relationship. Copying only one file from a multi-file disk can make the logical disk unavailable.
The disk created with a new virtual machine
The new-virtual-machine workflow normally supplies one virtual hard disk. The virtual machine configuration records that a virtual hard-disk device is attached and identifies the location of its VMDK storage.
The virtual machine itself is more than its disk. It includes configuration, virtual hardware definitions, and supporting files. The attached disk provides persistent guest storage, while the configuration tells VMware how to present that storage to the guest.
One disk is sufficient for many beginner installations, but additional disks can be useful for:
- Keeping application or project data separate from the operating-system disk.
- Testing partitioning, formatting, or storage software without changing the boot disk.
- Supporting a guest layout that uses separate system, data, or recovery disks.
- Giving a development or database workload a dedicated data disk.
Provisioned capacity versus host storage consumed
Virtual disk capacity is the maximum size presented to the guest. Host disk usage is the amount of space currently occupied by the virtual-disk files on the host filesystem.
For example, create an 80 GB growable virtual disk. The guest may report an approximately 80 GB drive immediately, even though the host initially stores only a much smaller amount of VMDK data. As the guest installs software and writes files, the host-side usage can increase toward the configured 80 GB limit.
This distinction does not remove the need to monitor host storage. A growable disk can expand unexpectedly, and several virtual machines can grow at the same time. Keep enough free space for possible disk growth, temporary guest activity, VMware supporting files, and the host operating system.
Growable virtual disks
A growable disk, also called thin-provisioned storage, starts with relatively low host-space usage and expands as the guest writes more disk blocks. Its configured maximum capacity remains an upper boundary; it does not automatically become larger than that limit.
- Benefit: Creation is usually faster because the host does not need to reserve the entire maximum size immediately.
- Benefit: Initial host-space consumption is reduced when the guest uses only part of the disk.
- Risk: The host volume can run out of free space as the disk grows.
- Risk: Multiple growable disks can compete for the same host storage.
For a practical comparison, a 60 GB growable development disk may initially occupy much less than 60 GB on a space-constrained laptop. That choice is useful only if you monitor free space and plan for the guest's future growth.
Preallocated virtual disks
A preallocated disk reserves its full configured capacity on the host when it is created. A 60 GB preallocated disk therefore requires approximately that amount of available host storage, plus reasonable operational headroom, before creation can complete.
Adding, reviewing, and changing virtual disks
Unless the product and guest explicitly support a hot storage change, fully power off the virtual machine before changing its virtual storage hardware. Do not treat a suspended VM as powered off for storage maintenance.
Review an attached disk
- Select the powered-off virtual machine in VMware Workstation Player.
- Open the virtual machine's settings.
- Select the hard-disk device.
- Review the configured capacity, storage location, connection state, and allocation-related options where the product exposes them.
Add another virtual disk
- Power off the VM completely.
- Open the VM settings and choose the control for adding hardware.
- Select a hard disk.
- Create a new disk or attach an existing compatible disk.
- Choose the intended capacity and allocation type when those options are presented.
- Start the guest and use its disk-management tools to rescan, initialize, partition, and format the new disk as appropriate.
Adding a disk in VMware does not automatically create a usable guest volume. The guest must detect the device and prepare it using its own storage tools.
Remove or detach a disk
Removing a hard-disk device from the VM configuration can mean detaching it: disconnecting the virtual hardware reference while leaving the underlying VMDK files on the host. Deleting the disk files is a separate and destructive action.
Before deleting files, confirm that the disk is no longer needed and make a backup if its data matters. If you only want the VM to stop using the disk temporarily, detach it rather than deleting it.
Moving and copying virtual disks
Because virtual disks are host files, they can be copied or moved to another folder, storage device, or compatible computer. Safe relocation requires more than dragging one visible file to a new location.
- Shut down the guest completely. Do not move an actively running or merely suspended VM.
- Copy the complete VM directory whenever possible, including its configuration and supporting files.
- If moving only a disk, copy the complete related VMDK file set, including its descriptor and extents when present.
- Preserve filenames and the directory relationships expected by the configuration.
- Confirm that the destination has enough free capacity for current data and possible growable-disk expansion.
- Open the relocated VM through its configuration file and verify that the hard disk is connected before relying on it.
Moving a virtual disk is not the same as moving the entire virtual machine. The full VM also includes configuration and other supporting files. Copying only a selected VMDK may omit required components or leave the VM configuration pointing to the former location.
Inspecting virtual-disk files on the host
To locate a VM's files, use VMware Workstation Player's VM settings to review the hard disk's storage location, then open that directory with the host's file browser. The exact folder depends on where the VM was created or moved.
A host file-browser view can demonstrate:
- The VM directory and its relationship to other VM files.
- The
.vmdkextension. - Whether multiple disk-related files belong to one logical disk.
- The real host-space usage of the files, which may be smaller than the capacity reported inside the guest.
Common virtual-disk management actions
Capacity planning and data protection
Choose virtual-disk capacity based on the guest operating system, applications, documents, updates, test data, and expected growth. A disk that is large enough for installation may still become inadequate after applications and project files are added.
- Leave meaningful free space on the host volume rather than planning only for the current VMDK size.
- Account for growth from every VM stored on the same host volume.
- Reserve room for temporary files, updates, snapshots, and other supporting VM data where applicable.
- Back up important virtual disks before relocation, deletion, resizing, or other structural changes.
- Treat a VMDK as important guest data, not as a disposable cache file.
Worked examples
Comparing guest capacity with host consumption
Create an 80 GB VM disk using growable allocation. The guest sees an approximately 80 GB drive. The host may initially store only a fraction of that amount. Install applications and copy files into the guest; as more blocks are written, the VMDK data can grow on the host. The guest's reported capacity stays near 80 GB throughout this process.
Adding a separate data disk
Power off the VM, add a second virtual hard disk through the VM hardware settings, and start the guest. In the guest operating system, rescan for hardware, initialize the disk if required, create a partition or volume, and format it. The second disk can then hold application data separately from the operating-system disk.
Choosing an allocation type
For a 60 GB development VM on a laptop with limited free space, growable allocation avoids reserving all 60 GB immediately, but requires careful monitoring. On a host with ample storage where a predictable reservation is preferred, preallocation reserves the full 60 GB at creation time.
Moving a VM
Shut down the VM rather than suspending it. Copy the complete VM folder to a destination with sufficient capacity, then open the VM from its configuration file at that destination. Keeping the complete folder together avoids missing related VMDK components and configuration references.
Troubleshooting virtual-disk problems
The host drive becomes unexpectedly full
- Likely causes: A growable disk expanded, multiple VMs share the volume, or maximum capacity was confused with current host usage.
- Check: Host free space and the sizes of VM directories and VMDK-related files.
- Resolution: Remove unnecessary guest data, move a VM to adequate storage, and plan for possible growth rather than only the current file size.
A moved VM cannot find its virtual disk
- Likely causes: Only part of a multi-file disk was copied, a component was renamed, or the configuration still points to the old location.
- Resolution: Restore the complete disk file set, keep related components together, and reconnect the intact existing disk through VM settings if necessary.
The guest does not show a newly added disk
- Likely causes: The disk was not connected in VM settings, the guest needs a rescan, or the disk has not been initialized and formatted.
- Resolution: Confirm the disk in the VM hardware list, then use the guest's disk-management utility to rescan, initialize, partition, and format it.
Important data disappeared after removing a disk
- Likely cause: The underlying files were deleted instead of merely detached, and no backup was available.
- Resolution: Stop further writes to the affected storage and restore from a known-good backup where available. Detaching a disk and deleting its files are different operations.
There is not enough space to create a preallocated disk
- Likely cause: The host volume lacks free space equal to the requested capacity plus operational headroom.
- Resolution: Choose a smaller disk, free host storage, select another destination, or use growable allocation if its risks are acceptable.
Exam-relevant summary
- A virtual disk is host-stored data presented to the guest as a disk device.
- VMDK is VMware's virtual disk format; one logical disk can use one file or multiple related files.
- A disk descriptor describes the disk, while extents hold its data.
- Guest-visible capacity is not the same as current host-space consumption.
- Growable disks use host space as data is written; preallocated disks reserve the configured capacity at creation.
- Detaching a disk removes its VM connection; deleting its host files destroys stored data.
- For relocation or backup, power off the VM and preserve the complete VM or complete associated disk file set.
- Always plan for host free space, disk growth, temporary activity, and backups.
For a concise reference, see Virtual Disks Explained.