VMware snapshots are a feature in VMware virtualization software that allows administrators to create a point-in-time copy of a virtual machine (VM). Snapshots allow administrators to roll back the VM to a previous state if something goes wrong.
Snapshots are useful in a variety of situations, such as:
- Testing software or making configuration changes to a VM without affecting the production version
- Capturing the state of a VM before performing maintenance or updates
- Rolling back a VM to a previous state if something goes wrong during an update or change
How do Snapshots Work
When a snapshot is taken, a new delta disk for the VM that stores all the changes made to the VM since the snapshot was taken is created. The delta disk is then linked to the original disk, forming a chain of disks.
For example, let’s say we have a VM with an original disk called “vm-disk-1.vmdk.” If we take a snapshot of the VM, VMware will create a new delta disk called “vm-disk-1-000001.vmdk” that stores all the changes made to the VM since the snapshot was taken. If we take another snapshot, VMware will create another delta disk called “vm-disk-1-000002.vmdk,” and so on.
The original disk and the delta disks are all linked together, forming a chain of disks. When the VM is powered on, VMware reads from the original disk and the delta disks, applying all the changes in the correct order.
Snapshots can be taken at any time, and multiple snapshots can be taken in a row. This allows administrators to create a kind of “undo” history for the VM, rolling back to previous snapshot states if necessary.
Virtual Machine Snapshot Benefits
There are several benefits to using snapshots for virtual machines (VMs):
- Easy recovery: vSphere snapshots allow administrators to quickly and easily roll back a VM to a previous state if something goes wrong. This can save a lot of time and effort compared to restoring from a backup or recreating the VM from scratch.
- Testing and development: vSphere snapshots can be used to test new software or make configuration changes to a VM without affecting the production version. This allows administrators to make changes in a controlled environment and roll back if necessary.
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Maintenance and updates: vSphere snapshots can be used to capture the state of a VM before performing maintenance or updates, allowing administrators to roll back if something goes wrong.
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Easy to use: vSphere snapshots are easy to create and manage, requiring minimal effort from administrators.
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Low overhead: vSphere snapshots have minimal impact on VM performance, allowing administrators to use them without affecting the performance of the VM.
vSphere snapshots are a useful tool for administrators to have in their toolkit, allowing them to easily roll back VMs to previous states if something goes wrong.
Are there any drawbacks to be aware of?
While snapshots can be a useful tool for virtual machine (VM) management, there are also some negative aspects to consider:
- Disk space: vSphere snapshots can consume a lot of disk space, as each snapshot creates a new delta disk that stores all the changes made to the VM since the snapshot was taken. This can lead to disk space shortages if snapshots are not managed properly.
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Complexity: vSphere snapshots can create a chain of disks that can be difficult to manage, especially if there are many snapshots in the chain.
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Limited protection: vSphere snapshots are not a replacement for proper backups. While snapshots can be useful for rolling back a VM to a previous state, they do not protect against data loss due to hardware failures or other disasters. It’s important to have a proper backup strategy in place to protect against these types of events.
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Limited retention: vSphere snapshots are not meant to be a long-term storage solution and are typically only retained for a few days or weeks.
Overall, while vSphere snapshots can be a useful tool for VM management, it’s important to use them judiciously and to have a proper backup strategy in place to protect against data loss. It’s also important to regularly monitor and delete old snapshots to free up disk space and maintain good performance.
How to Create a vSphere Virtual Machine Snapshot
To create a VMware vSphere snapshot for a virtual machine (VM), follow these steps:
- Connect to your vSphere environment using the vSphere Web Client.
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In the inventory tree, navigate to the VM for which you want to create a snapshot.
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Right-click the VM and select “Snapshot.”
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In the “Create Snapshot” dialog box, enter a name and optional description for the snapshot.
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Select the “Memory” and “Quiesce guest file system” options if you want to include the VM’s memory state and quiesce the file system in the snapshot.
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Click “OK” to create the snapshot.
Once the snapshot has been created, it will appear in the snapshot manager for the VM. From here, you can manage the snapshot (e.g., rename, delete, or revert to the snapshot).
What does Quiesce Guest Filesystem Mean
The the section above it was mentioned that there is an option to “Quiesce guest file system” when creating a virtual machine snapshot.
Quiescing a file system means to temporarily pause all write operations to the file system, allowing a consistent state to be captured. This is typically done in order to create a consistent snapshot or backup of the file system.
In the context of VMware snapshots, quiescing the file system means that all write operations to the file system of the virtual machine (VM) will be temporarily paused while the snapshot is being taken. This ensures that the snapshot is a consistent and coherent point-in-time copy of the VM, with all data written to the file system at the time the snapshot was taken.
Quiescing the file system is done using VMware Tools installed on the guest virtual machine. It sends a request to the operating system to pause all write operations to the file system, allowing the snapshot to be taken, helping to protect against any data being lost or corrupted.
Manage vSphere Virtual Machine Snapshots using PowerCLI
VMware PowerCLI is a command-line interface that allows administrators to automate and manage VMware vSphere environments using PowerShell.
Create a Snapshot Using PowerCLI
Here are the steps to create and delete snapshots using PowerCLI:
To create a snapshot: Connect to your vSphere environment using PowerCLI. You can do this using the following command:
Connect-VIServer -Server "vcenter server" -User "username" -Password "password"
Use the New-Snapshot cmdlet to create a snapshot of a VM. Here is the basic syntax:
New-Snapshot -VM "vmname" -Name "snapshot name" -Description "description"
For example, to create a snapshot of a VM called “myvm” with the name “snapshot1” and a description of “test snapshot,” you would use the following command:
New-Snapshot -VM myvm -Name snapshot1 -Description "test snapshot"
Delete a Snapshot Using PowerCLI
To delete a snapshot, use the Get-Snapshot cmdlet to list the snapshots for a VM. Here is the basic syntax:
Get-Snapshot -VM "vmname"
Use the Remove-Snapshot cmdlet to delete a snapshot. Here is the basic syntax:
Remove-Snapshot -Snapshot "snapshot object"
For example, to delete the snapshot “snapshot1” for the VM “myvm,” you would use the following command:
Remove-Snapshot -Snapshot (Get-Snapshot -VM myvm | Where-Object {$_.Name -eq "snapshot1"})
Note: Be careful when deleting snapshots, as they can be a useful tool for rolling back a VM to a previous state. It’s important to have a proper backup strategy in place to protect against data loss.
How to List All Snapshots using PowerCLI
To list all snapshots in a VMware vSphere environment using PowerCLI, you can use the Get-Snapshot cmdlet. Here is the basic syntax:
Get-Snapshot
This will return a list of all snapshots in your vSphere environment. If you want to list the snapshots for a specific VM, you can use the -VM parameter and specify the name of the VM. For example, to list the snapshots for the VM “myvm,” you would use the following command:
Get-Snapshot -VM myvm
You can also use the Where-Object cmdlet to filter the snapshots based on certain criteria. For example, to list all snapshots with a name that starts with “snapshot1,” you could use the following command:
Get-Snapshot | Where-Object {$_.Name -like "snapshot1*"}
Virtual Machine Snapshots vs Backups
A VMware snapshot and a backup are two different things that serve different purposes. Here are some key differences between a VM snapshot and a backup:
- Purpose: A VM snapshot is a point-in-time copy of a VM that can be used to roll back the VM to a previous state if something goes wrong. A backup, on the other hand, is a copy of data that is used to restore data in the event of data loss due to hardware failure, disaster, or other reasons.
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Retention: VM snapshots are typically only retained for a few days or weeks, while backups can be retained for longer periods of time (e.g., months or years).
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Recovery time: It is usually faster to recover a VM from a snapshot than from a backup, as snapshots are stored on the same storage as the VM and do not require the data to be restored from a separate location.
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Data protection: VM snapshots do not protect against data loss due to hardware failure or other disasters. Backups, on the other hand, are specifically designed to protect against data loss and can be stored on separate storage or in a different location for added protection.
VM snapshots are a useful tool for quickly rolling back a VM to a previous state, but they are not a replacement for proper backups. It’s important to have a proper backup strategy in place to protect against data loss and to ensure that data can be restored in the event of a disaster.
Reverting a Snapshot
Reverting to a snapshot means rolling back a virtual machine (VM) to the state it was in when the snapshot was taken. This is typically done if something goes wrong with the VM and you want to return it to a previous, known-good state.
When you revert to a snapshot, the changes made to the VM since the snapshot was taken are discarded, and the VM is returned to the state it was in when the snapshot was taken. This includes the configuration, data, and state of the VM at the time the snapshot was taken.
To revert to a snapshot, you can use the VMware vSphere Client or PowerCLI. Here is the basic process using the web client:
- Connect to your vSphere environment using the vSphere Web Client.
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In the inventory tree, navigate to the VM for which you want to revert to a snapshot.
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Right-click the VM and select “Snapshot.”
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In the snapshot manager, select the snapshot you want to revert to and click “Revert.”
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Confirm the revert operation.
The revert process may take a few moments to complete, depending on the size of the VM and the amount of changes made since the snapshot was taken.
It’s important to note that reverting to a snapshot can result in data loss, as any changes made to the VM since the snapshot was taken will be discarded. It’s important to use caution when reverting to a snapshot and to have a proper backup strategy in place to protect against data loss.
Summary
Overall, VMware snapshots are a useful tool for administrators to have in their toolkit, allowing them to easily roll back VMs to previous states if something goes wrong. However, it’s important to use them judiciously and to have a proper backup strategy in place to protect against data loss.