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In this article by Sander van Vugt, author of VMware Workstation – No Experience Necessary, you'll learn to work with cloning and snapshot tools. In a test environment, it is often necessary to deploy virtual machines rapidly and to revert to a previous state in an easy way. VMware Workstation provides all the tools that are required for this purpose. In this article, you'll learn to work with cloning and snapshot tools that enable you to perform these tasks.
(For more resources related to this topic, see here.)
Understanding when to apply which tools
A snapshot is a photo of a state of a virtual machine. As a virtual machine often requires a lot of work before a desired state of the machine is reached, it is a good idea to take a picture of that exact state. If something goes wrong at a later stage, having a snapshot makes it possible to easily revert to the previous state of the virtual machine. So the base concept of working with snapshots is to make it easier to revert to a previous state.
A clone is a copy of a virtual machine. Using clones is convenient if several virtual machines are needed, with more or less the same configuration on each virtual machine. By cloning a virtual machine, you'll make a copy of the actual state of a machine. After making the clone, you'll just have to modify the properties of the virtual machine that need to be unique on that machine.
In some ways, clones and snapshots are closely related. This is because you can create a clone of a snapshot of a virtual machine, but you can also clone the current state of a virtual machine, which in fact creates a snapshot of the virtual machine. To understand this, you need to understand the difference between a linked clone and a full clone.
In a linked clone, only modifications are stored. This means that if something happens to the original state of the virtual machine (for example, the VM files get corrupted), the linked clone gets corrupted as well. It is, however, an approach that is very efficient with regard to available disk space. As only modifications are stored in a linked clone, the disk space requirement is minimal. Creating a linked clone is also a very fast process.
A full clone is like a complete copy of a virtual machine. Creating a full clone is a much longer process as the entire virtual machine disk has to be copied over. It requires more disk space as well, but the benefit is that a full clone creates an independent virtual machine. Therefore, you're better off with full clones if you need a maximum amount of flexibility. You'll also learn how to work with snapshots and clones.
Working with snapshots
In this article, you'll learn how to create snapshots of virtual machines. You'll also learn how to use the Snapshot Manager to manage a setup where different snapshots are used.
To create a snapshot, you don't have to do anything with the virtual machine. You can create a snapshot irrespective of the actual state of the virtual machine, so it doesn't matter if it is currently active or not. If the machine is powered on, the current state of the virtual machine memory is included in the snapshot as well. This is a useful feature as it allows you to return to the exact state the machine was in while taking the snapshot.
To create a snapshot of a virtual machine, select the virtual machine first. Then from the VM menu, navigate to Snapshot | Take snapshot. Here you are presented with a small dialog box where you can enter a short description of the snapshot. You should always enter some description as it may be clear now what the snapshot is being used for, but you probably won't know it anymore if you have a look at the virtual machine a few months later. Also, having a clear description for a snapshot makes it easier to identify the right snapshot in the Snapshot Manager.
To make identifying the snapshot easier at a later stage, enter a clear description of what it is being used for
Once the snapshot process has started, it will take a while to complete. You will see a progress bar in the lower-left part of the virtual machine window if it has been activated. In theory, you can just continue working in the virtual machine; in practice, you'll notice that it is slow and sometimes even very unresponsive. It's better to wait a while and give the snapshot process a few minutes to complete.
The actual files of the snapshots will be created in the directory where the VMDK files of the virtual machine are stored. For each VMDK file, you'll find a snapshot file as well. You'll notice that the snapshot file is smaller as it only contains the modifications that were made since the last snapshot was taken; or if this is the first snapshot you have taken, it will contain the differences from the original virtual machine.
For each VMDK file, a corresponding snapshot file is created
Working with the Snapshot Manager
The Snapshot Manager allows you to work with snapshots in the most flexible way. You can use it to revert to any virtual machine state, start from there, and build a completely different configuration so that you can create two development branches based on a specific snapshot state and decide which solution fits you best.
You can find the Snapshot Manager by opening the virtual machine you want to manage and navigating to VM | Snapshot | Snapshot Manager. You'll now see the Snapshot Manager with all the snapshots that have been created for this virtual machine.
The Snapshot Manager allows you to revert to any state of a virtual machine
Working with snapshots from the Snapshot Manager is not hard to do at all. You'll just select the snapshot that you want to start from and restore it (irrespective of whether there are snapshots that have already been created based on the selected snapshot). Once restored, you can continue working on the virtual machine from the selected snapshot state.
By default, in the Snapshot Manager you don't see autoprotect snapshots. Even if the Snapshot Manager shows an option that displays autoprotect snapshots as well, it is probably not a good idea to do that. You'll typically use the snapshots in Snapshot Manager to walk back a clearly defined path in the snapshots on your system. In autoprotect, there isn't really a plan, and even more importantly, the snapshots are removed automatically. Therefore, you should make sure to never create a snapshot that is based on an autoprotect snapshot.
A snapshot is a virtual machine that is in a specific state. When working with snapshots, there will still be one virtual machine that can easily be restored to a specific state. The major difference between a clone and a snapshot is that a clone is a new virtual machine that is independent of the original virtual machine. Even if there is some relation between a snapshot and a clone (for instance, you can create a clone based on a snapshot), a clone basically is a new virtual machine. This means that once you have created a clone of a virtual machine, you can even start creating new snapshots of that virtual machine.
When creating clones, you really need to think well about what you want to use them for. If you just want to use them for your own convenience, a linked clone is the best solution. It can be created very fast, and it takes the least possible amount of disk space while it still offers full functionality. The major difference though is that you'll never be able to copy it as an independent virtual machine to another computer. If you need to do that, you'll need a full clone.
There are different ways to create clones. No matter which method you use, you will have to make sure that the virtual machine is shut down before you can make the clone. This requirement exists because the virtual machine files cannot be modified while the cloning is in process. The most important reason for this is that VMware Workstation is used on a Linux host or Windows platform where filesystems are used that do not allow virtual machine files to be modified by different processes at the same time. You'll need a VMFS filesystem in a VMware ESXi environment if you want to be able to clone a virtual machine without shutting it down first.
The most direct way of creating a clone is by using the Manage option in the VM menu. From this menu, select the Clone option to start the Clone wizard. The first step of the clone wizard asks where you want to create the clone from. This can either be from the actual state of the virtual machine or from a snapshot, if it has been created. If no fit snapshot exists, the wizard will show an error, indicating that it's not possible to create a clone based on a snapshot for the selected virtual machine.
Selecting on the basis of what you want to clone
After selecting what you want to create the clone on, you'll need to select between either a linked clone or a full clone. You have to realize that a full clone is a complete copy of a virtual machine, so you'll need the same amount of disk space that is used by the virtual machine as available disk space on the host computer. So if the virtual machine uses 60 gigabytes of disk space, you'll need at least 60 gigabytes of disk space on the host as well!
After verifying that you have the required amount of free disk space, you can start the cloning process. In the last step of the wizard, specify the name that you want to assign to the clone as well as the location on the host operating system where the clone has to be stored. Once created, the clone will show in the VMware console as a new virtual machine, and that is also how it is to be considered.
A cloned virtual machine appears as a completely new virtual machine in the VMware Workstation library
Another way of creating clones is using the Snapshot Manager. The advantage is that using Snapshot Manager, you can easily select a snapshot that you want to create a clone of. Just select the snapshot state you want to use and click on the Clone button.
In this article, you learned how to work with cloning and snapshots of tools. You learned how to create snapshots and clones, and work with snapshot manager.
Resources for Article:
- VMware View 5 Desktop Virtualization [Article]
- Creating an Image Profile by cloning an existing one [Article]
- Installing Zenoss [Article]
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About the Author :
Sander van Vugt is an independent author, consultant, and technical trainer, living in Netherlands. He is specialized in open source software and virtualization. He has written over 50 books on many subjects, most of them about Linux. As a consultant he has realized numerous projects involving open source software and virtualization for different companies around the world. You can find more information about him on his website, www.sandervanvugt.com.