VMware File Types Explained: VMDK, VMEM, VMSN, VMSD, VMX & More

by David Davis - January 8, 2009

When using VMware Server & Workstation, you will, at some point, go to the directory where your VMware virtual machines are stored. Inside this directory, you will see a number of strange files and you will probably wonder what they are and what they do. Now, you can stop wondering and find out.

Directory Listing

Below, you’ll see a typical VMware directory listing of a folder where VMware virtual machines are stored.

Here is the command prompt version of the same directory listing:

In this directory, you’ll notice a number of different files types. There are log files, vmdk files, vmem files, vmsn, nvram, vmsd, and vmx files. In fact, there may be other types of files. Some of these files are very small, while others are very large. Let’s learn about each of these VMware files.

Files you should know

Log files – Log files are just that- a log of virtual server activity for a single virtual server. Here is an example of what a log file looks like:

Log files should be used only when you are having trouble with a virtual machine.

VMDK files – VMDK files are the actual virtual hard drive for the virtual guest operation system (virtual machine / VM). You can create either dynamic or fixed virtual disks. With dynamic disks, the disks start small and grow as the disk inside the guest OS grows. With fixed disks, the virtual disk and guest OS disk start out at the same (large) disk. For more information on monolithic vs. split disks see this comparison from sanbarrow.com.

VMEM – A VMEM file is a backup of the virtual machine’s paging file. It will only appear if the virtual machine is running, or if it has crashed.

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VMSN & VMSD files – these files are used for VMware snapshots. A VMSN file is used to store the exact state of the virtual machine when the snapshot was taken. Using this snapshot, you can then restore your machine to the same state as when the snapshot was taken. A VMSD file stores information about snapshots (metadata). You’ll notice that the names of these files match the names of the snapshots.

NVRAM files – these files are the BIOS for the virtual machine. The VM must know how many hard drives it has and other common BIOS settings. The NVRAM file is where that BIOS information is stored.

VMX files – a VMX file is the primary configuration file for a virtual machine. When you create a new virtual machine and answer questions about the operating system, disk sizes, and networking, those answers are stored in this file. As you can see from the screenshot below, a VMX file is actually a simple text file that can be edited with Notepad. Here is the “Windows XP Professional.vmx” file from the directory listing, above:

You can actually download VMX files, based on answers you create, from the Internet. Here are some websites that allow you to do this: EasyVMX! VM Builder vmx-builder.cmd

Summary

In summary, it is important to know the different types of VMware files. You never know when you need to edit a configuration file manually. Or, perhaps, you just want to know why a certain file is taking up so much disk space. Either way, this guide to VMware disk values should be kept handy. Of particular interest are VMX files and VMDK files. Both of these can be downloaded from the Internet to instantly create a complete virtual server. For more information, see this VMware article explaining what files make up a virtual machine.

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