Files that make up a virtual machine (VM) – Back to Basics

A VM is encapsulated in files that contain all hardware and software states running within the VM. Below are the various VMware file types associated with a VM, located in the VM’s directory on the host


Here is each file type in detail.

  • vmdk: Corresponds to a metadata file. The virtual disk description (editable file) provides the link to the .flat-vmdk file.
  • flat-vmdk: The most important file because it is the VM’s virtual disk and contains all the data for the VM: operating system, applications, and so on.
  • vmx: Contains all configuration information and material parameters for the VM, such as memory size, hard drive size, network card information, and MAC address. It is the first file created when a VM is created.
  • nvram: Contains the VM’s BIOS status.
  • log: Tracks the VM’s activity. Several log files exist, and they are very useful for diagnosing problems. VMware’s support services use them. A new log file is created when the VM is shut down and restarted or when the file reaches its maximum size, as defined in advanced configuration options (vCenter’s advanced options: log.rotate size and logkeepOld).
  • vmss: Created when a VM is suspended. This file contains the entire content of the active memory. When the VM is put back into service, the content of the vmss file returns to the server’s RAM, which creates a work environment identical to the one that existed before the VM was suspended.
  • vswp: Automatically created whenever a VM starts. This file is used as the VM’s memory swap. A VM cannot start if this file cannot be created.

When snapshots are initialized, the following file types are created:

  • -delta.vmdk: Created and used when taking a VM snapshot. At the moment the snapshot is created, the original vmdk file is quiesced and put into read-only mode. No more data will be written into this original file. For example, 00000#.vmdk contains the metadata associated with the snapshot.
  • vmsd: Contains snapshot information and metadata, including the name of the associated vmdk and vmsn. A file is created that contains all the information from all snapshots. A vmsn file is created for each snapshot. Filenames follow numeric increments. For example, Snapshotxxx.vmsn contains the state of the snapshot that contains the running VM’s status at the moment the snapshot is taken.

Other files:

  • hlog: Log files for vMotion.
  • RDMv: Raw device mapping in virtual compatibility mode.
  • RDMp: Raw device mapping in physical compatibility mode.
  • vSphere HA: A special folder that includes special files. For example, host-xxx-hb, Poweron, and Protectedlist are special files used by vSphere HA for Heartbeat and for the consistency of protected VMs.
  • mvtx: For templates.
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