What is VMware file format?

VMware file format refers to the different file types and extensions used by VMware products, primarily VMware Workstation, ESXi, and vSphere. These file formats allow VMware products to create, manage, and run virtual machines and templates.

What is VMware file format?

Common VMware File Types and Extensions

Some of the most common VMware file formats include:

  • VMDK: Virtual Machine Disk format, represents a virtual hard disk drive. Allows virtual hard disks to be portable between systems.
  • VMX: Contains configuration data for a virtual machine. Defines resources like CPU, memory, network, and storage.
  • OVA/OVF: Open Virtualization Format, an open standard for packaging and distributing software applications for virtual machines.
  • VMEM: Files containing snapshots of a virtual machine’s memory state. Used to restore VMs to saved state.
  • NVRAM: Stores BIOS configuration of a virtual machine.
  • LOG: Log files that record activity and events ocurring inside a virtual machine.

Benefits of VMware’s File Formats

VMware’s proprietary file formats offer several benefits:

  • Portability – Files can be easily moved between VMware products and platforms.
  • Performance – Designed to optimize virtual machine performance.
  • Flexibility – Modular file types enable flexibility in configuring virtual machines.
  • Backwards Compatibility – New versions of VMware products support older file formats.

Key VMware File Format – VMDK

The most important VMware file format is the VMDK or Virtual Machine Disk format. Here are some key details about VMDK files:

  • Used for virtual hard disk storage, analogous to a physical hard drive.
  • Contains the operating system, applications, data files for a VM.
  • Has either a .vmdk or .VMDK file extension.
  • Has variants like monolithic or split disk types.
  • Can be copied, transported, backed up, like a physical hard disk.
  • Supported across VMware desktop and enterprise platforms.

Types of VMDK Files

There are 2 main types of VMDK files:

  • Monolithic: Stores virtual disk data in a single file. Ideal for smaller drives.
  • Split: Splits the disk data across multiple files enabling larger drive sizes.

Split VMDKs use additional files with extensions like .vmdkdescriptor and .vmdkflat.

VMDK File Contents

Inside, VMDK files resemble a physical hard drive with the following components:

  • MBR – Master Boot Record
  • Partitions – Split virtual hard disk into logical segments.
  • File System – Organizes data files e.g. NTFS or EXT4
  • Virtual Data Files – Actual data stored on the virtual disks.

This internal structure allows the VMDK to boot, install, and run operating systems and programs like a physical computer.

Leveraging VMware File Formats

Understanding VMware’s file types allows users to better leverage them across functions like:

  1. Transporting Virtual Machines

A key benefit of VMDK files is portability. Users can easily move VMs between:

  • Multiple hosts – Migrate VMs across ESXi or Workstation hosts.
  • On-prem and Cloud – Upload VMDK based VMs to VMware cloud.
  • Platform conversions – Convert VMDK based VMs across desktop, datacenter, and cloud.
  1. Backing-up and Restoring

VMDK files can be backed up or snapshotted to retain point-in-time copies of a VM state. Snapshots generate a set of files allowing users to restore VMs to previous configurations.

  1. Cloning and Templates

Using files like VMX and VMDK, IT teams can rapidly deploy VMs by cloning templates. This can accelerate environment spin-up.

  1. Migrating Physical Systems

Physical systems can be converted to virtualized VMDK drives allowing migration from physical to virtual machines.

Key Takeaways

  • VMware uses proprietary file formats like VMDK, OVF, VMX to support virtualization functions.
  • VMDK is the most widely used format that encapsulates an entire VM hard drive.
  • File portability provides flexibility in moving VMs across environments.
  • Files like VMDK can be backed up, snapshotted, and restored.
  • Templates allow IT teams to clone and deploy new VMs rapidly.


In summary, VMware utilizes open and proprietary file formats to enable virtual machine portability and flexibility across platforms. The virtual disk file type, VMDK, is the most essential format that encapsulates an entire VM hard drive. Understanding these formats helps users optimize VMware deployment, migration, backup, disaster recovery and scaling.

Frequently Asked Questions

  1. What is a VMDK file?
    A VMDK file is a VMware virtual hard disk file that encapsulates an entire operating system, applications, user data to emulate a real hard drive. It is the most common VMware file type.
  1. How is a VMware virtual disk different from physical disk?
    A VMware virtual disk stored as a VMDK has a similar internal structure as physical hard drive but the data is stored in a portable file rather than on physical platters.
  1. What is the difference between monolithic and split VMDK?
    Monolithic VMDKs store disk data in a single file while split VMDKs split data across multiple files enabling larger drive sizes.
  1. Can a VMDK file be used on any hypervisor like HyperV or VirtualBox?
    No, VMDK files can only be used on VMware products like vSphere, Workstation, or Fusion. They are not compatible with other hypervisors.
  1. How can you transport VMDK files between environments?
    VMDK files can be transported by copying them to external disks or uploaded to products like VMware Cloud. They retain full functionality when moved.
  1. What VMware file extension is used for virtual machine configuration?
    The .VMX file extension contains configuration data for a virtual machine, defining CPU, memory, network and other parameters.
  1. How are OVA and OVF files different from VMDK?
    OVA and OVF files package an entire virtual machine for distribution and deployment across VMware platforms.
  1. Which VMware file type is used to store BIOS settings of a VM?
    The NVRAM file extension stores BIOS and system firmware configuration settings for a virtual machine.
  1. What file type contains snapshot data to restore VM state?
    VMEM files contain snapshots of the VM’s memory state and can be used to revert back to saved system restore points.
  1. How do VMware logs files help troubleshoot virtual machine issues?
    The VMware LOG files record detailed event activity and allows administrators to review them to troubleshoot operational issues.
  1. Can physical machine backups be converted to VMDK files?
    Yes, physical systems and drive images can be transformed into the VMDK format for migration into VMware virtualized environments.
  1. Is a VMDK file larger or smaller than the data it actually stores?
    VMDK files utilize space optimization techniques so are typically slightly smaller than source data size.
  1. Do all guest operating systems work with VMDK disk files
    VMDK files work with all guest operating systems supported by VMware including Linux, Windows, BSD, etc.
  1. Can a VMDK disk file be partitioned and formatted just like physical disk?
    Yes, once attached to a virtual machine, VMDK can be partitioned, formatted, and managed through OS just like a physical disk.
  1. How does VMware improve performance of VMDK disk access?
    Techniques like I/O caching, sequentialization, native command queuing help improve virtual disk performance.
  1. What is the maximum size for VMDK files?
    The maximum size supported for VMDK virtual disks is 64TB. But this limit also depends on VMware product capabilities.
  1. How can you expand capacity of an existing VMDK disk?
    Using the Edit Settings option, users can expand the storage capacity allocated to an existing VMDK file.
  1. Is a VMDK sparse file? What are benefits?
    Yes, VMDK files utilize sparse allocation meaning space is allocated as needed via thin provisioning to improve storage efficiency.
  1. Can VMware Workstation open ESXi server VMDK files
    Yes, VMware Workstation can directly access, open and convert ESXi hosted VMDK files to local Workstation machines.
  1. Is vMotion used to migrate VMs dependent on VMDK files?
    Yes, features like vMotion, Storage vMotion rely on VMDK file contents being migrated across storage locations.


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