Weekly Quick Tip: VMware's File Extensions Explained

Need a quick primer? Greg gives a rundown.

If you use VMware in virtually any of its flavors, then you've probably become familiar with the list of files created in each folder you create for a virtual machine (VM). Those listed files are used by the software to process the running of each VM. But what exactly is each file for? What does each do? Let's take a few minutes to look at the file extensions that you'll see within each VM's folder to help you understand the role of each.

.VMDK: These files are the actual hard disk of the VM itself, and tend to be the largest file within the folder. You can consider the size of these files to be roughly equivalent to the size of either the disk itself, if you've chosen to use pre-allocated disks; or the size of the data currently stored on that disk, if you use "growable" disks.

.NVRAM: Consider this file the BIOS of the VM.

.VMX: With typically one .VMX file per folder, this file holds the configuration information for the VM in a text format. Unlike almost all the other files you'll see, .VMX files can be edited using any text-editing program, a process that's actually required for some functionality that's not exposed in the GUI.

.VMXF: This file, in XML format, includes additional information about the VM if it has been added to a team. If a machine has been added to a team and then later removed, this file remains resident. This file can also be opened and read in a text editor.

.VMTM: For VMs actively participating in a team, this file stores information about that team membership.

.VMEM: These files, which contain a backup of the VM's paging file, are typically very small or nonexistent when the VM is powered off, but grow immediately to the size of configured RAM when the machine is powered on.

.VMSN and .VMSD: When snapshots are created for a VM, these files are created to host the state of the VM. The .VMSN file stores the running state of the machine: what you could consider the "delta" between the .VMDK at the point of the snapshot and what has been processed up until the present time. The .VMSD stores information and metadata about the snapshot itself.

.VMSS: If you've suspended the state of your machine, this file contains the suspended state of that machine. These files typically appear only when VMs have been suspended.

Depending on the VMware product you use or the platform upon which it resides, these files may be slightly different.

However, these files are mostly the same across all versions of VMware's products.

About the Author

Greg Shields is a senior partner and principal technologist with Concentrated Technology. He also serves as a contributing editor and columnist for TechNet Magazine and Redmond magazine, and is a highly sought-after and top-ranked speaker for live and recorded events. Greg can be found at numerous IT conferences such as TechEd, MMS and VMworld, among others, and has served as conference chair for 1105 Media’s TechMentor Conference since 2005. Greg has been a multiple recipient of both the Microsoft Most Valuable Professional and VMware vExpert award.

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