Let’s talk about snapshots! Snapshots Explained!

A VMware snapshot is a point-in-time copy of the virtual machine’s state, including its virtual disk files and configuration. Snapshots are used to capture the state of a virtual machine at a specific point in time, so that you can revert to that state later if needed.

Snapshots are often used for the following purposes:

  • Testing: Snapshots can be used to create a safe test environment, allowing you to make changes to a virtual machine and then revert back to the snapshot if the changes cause problems.
  • Development: Snapshots can be used to allow multiple developers to work on a virtual machine simultaneously, allowing each developer to make changes and then revert back to the snapshot when their work is complete.
  • To create a point-in-time short-time backup of a virtual machine, allowing you to restore the virtual machine to a previous state if something goes wrong.

NOTE: SNAPSHOTS ARE NOT BACKUPs!

Snapshots are not a replacement for a proper backup strategy. While snapshots can be useful for creating a point-in-time copy of a virtual machine’s state, they have some important limitations that make them unsuitable as a primary method for protecting your data:

  • Snapshots are not independent of the virtual machine: Snapshots are stored as changes to the virtual machine’s disks, and they depend on the underlying virtual machine files to be complete. This means that if something goes wrong with the virtual machine files, the snapshot may be lost or become unusable.
  • Snapshots can consume a lot of disk space: As you create and delete snapshots, the virtual machine’s disks can become fragmented, and the snapshot files can grow in size. This can lead to significant disk space consumption, which can impact the performance of the virtual machine and other virtual machines on the same host.
  • Snapshots can impact performance: As the number of snapshots increases, the virtual machine’s performance may suffer. This is because each snapshot requires additional disk space, and the virtual machine must read and write data to both the original disks and the snapshot disks when it writes data.

For these reasons, it’s important to use snapshots judiciously and to plan carefully when using them in your environment. While snapshots can be a useful tool, they should not be relied on as the sole method for protecting your virtual machines and data. Instead, you should use a combination of snapshots and other backup and recovery methods, such as regular backups to external storage, to ensure the integrity and availability of your data.

How do Snapshots Work?

When you create a snapshot of a virtual machine, the snapshot captures the state of the virtual machine’s disks and configuration at that point in time. The snapshot stores the changes to the virtual machine’s disks that have occurred since the previous snapshot, if any. This disk is called a delta disk.

Snapshot delta disks are used to track changes made to a virtual machine’s disks after a snapshot is taken. When the virtual machine writes data to its disks, the data is also written to the snapshot delta disk. This allows the snapshot to capture a point-in-time copy of the virtual machine’s state, including its disks and configuration.

Snapshot delta disks are stored in the same location as the virtual machine’s disks, and they are named with a “.vmdk” file extension. They are typically small when compared to the size of the virtual machine’s disks, as they only store the changes made since the previous snapshot.

NOTE: It’s important to note that snapshot delta disks can consume a significant amount of disk space over time, especially if the virtual machine is actively writing data and you are taking frequent snapshots. As such, it’s important to regularly delete unnecessary snapshots and to plan carefully when using snapshots in your environment to avoid running out of disk space.

The original virtual machine disk and the snapshot delta disks are linked together in a chain, with the changes recorded in the delta disks being applied in the correct order to the original disk when the virtual machine is powered on. This allows the virtual machine to access a point-in-time copy of its disks and configuration that was captured when the snapshot was taken.

How to Create a vSphere Virtual Machine Snapshot using the vSphere Web Client.

To create a snapshot of a virtual machine using the vSphere Web Client:

  1. Open the vSphere Web Client and log in to your vCenter Server.
  2. Navigate to the inventory object for the virtual machine that you want to snapshot. This could be a host, a cluster, or a resource pool.
  3. Right-click on the virtual machine and select “Snapshot” from the menu.
  4. In the “Create Snapshot” dialog, enter a name and description for the snapshot.
  5. (Optional) Check the “Quiesce guest file system” option to freeze the virtual machine’s file system and create a consistent snapshot. This is recommended for applications that support quiescing, as it ensures that the snapshot captures a consistent state of the virtual machine’s disks.
  6. (Optional) Check the “Memory” option to include the virtual machine’s memory state in the snapshot. This can be useful for creating a snapshot of the virtual machine’s state at a specific point in time, but it can also significantly increase the snapshot file size.
  7. Click “OK” to create the snapshot.

It may take a few minutes for the snapshot to be created, depending on the size of the virtual machine’s disks and the amount of data that has changed since the previous snapshot.

Once the snapshot has been created, it will appear in the snapshot manager for the virtual machine. You can use the snapshot manager to view, delete, or revert to the snapshot as needed.

What is the “Include virtual machine’s memory” option for?

The “Include virtual machine’s memory” option is a setting that you can select when taking a snapshot of a virtual machine using VMware vSphere or other VMware management tools. When this option is selected, the snapshot will include the virtual machine’s memory state in addition to its disks and configuration.

Including the virtual machine’s memory state in the snapshot can be useful in some cases, such as when you want to capture the exact state of the virtual machine at a specific point in time. For example, if you are debugging a problem with the virtual machine and want to capture its memory state as part of the snapshot, you can select this option to include the memory state in the snapshot.

However, it’s important to note that including the virtual machine’s memory state in the snapshot can significantly increase the size of the snapshot and the time it takes to create the snapshot. It can also impact the performance of the virtual machine while the snapshot is being taken. As such, it’s important to consider the potential performance and space implications when deciding whether to include the virtual machine’s memory state in the snapshot.

What does Quiesce Guest Filesystem Mean?

Quiescing a guest file system means freezing the file system to ensure a consistent snapshot. When you quiesce the guest file system, the virtual machine’s operating system is paused briefly while the snapshot is taken. This allows the snapshot to capture a consistent view of the file system, including open files and in-flight transactions.

Quiescing the guest file system is typically recommended when taking a snapshot of a virtual machine that is running a database or other application that requires a consistent view of the file system. It can help ensure that the snapshot captures a consistent and usable state of the virtual machine.

To quiesce the guest file system when taking a snapshot of a virtual machine, you can select the “Quiesce guest file system” checkbox in the “Create Snapshot” dialog. This option is available when creating a snapshot using the vSphere Web Client or other VMware management tools.

It’s important to note that quiescing the guest file system can impact the performance of the virtual machine, as it requires the virtual machine’s operating system to pause briefly while the snapshot is taken. As such, it’s important to consider the performance implications when deciding whether to quiesce the guest file system.

Quiescing the file system is a process that involves using VMware Tools to pause write operations to the guest virtual machine’s file system while a snapshot is taken. This helps to ensure that the snapshot captures a consistent view of the file system and helps to protect against data loss or corruption. To quiesce the file system, VMware Tools sends a request to the guest virtual machine’s operating system to pause write operations while the snapshot is taken.

How to revert a snapshot using the vSphere Web Client:

  1. Navigate to the virtual machine that has the snapshot you want to revert to.
  2. Right-click on the virtual machine and select “Snapshot” from the context menu.
  3. In the Snapshot Manager window, select the snapshot you want to revert to and click the “Revert” button.
  4. A dialog box will appear asking you to confirm the revert operation. Click “Yes” to proceed.
  5. The virtual machine will be reverted to the selected snapshot.

Create a Snapshot Using PowerCLI

To create a snapshot using PowerCLI, you will need to have the PowerCLI tool installed on your system and be connected to a vSphere environment. Here is an example of how you can create a snapshot using PowerCLI:

  1. First, connect to your vSphere environment using the Connect-VIServer cmdlet:
Connect-VIServer -Server vcenter.example.com -User administrator@example.com -Password mypassword
  1. Use the New-Snapshot cmdlet to create a snapshot for the virtual machine:
New-Snapshot -VM vmmane -Name "Snapshot Name" -Description "Snapshot Description"
  1. You can verify that the snapshot was created successfully by using the Get-Snapshot cmdlet:
Get-Snapshot -VM "vmname"

NOTE: You can also include the virtual machine’s memory and quiesce the file system with Powershell :

New-Snapshot -VM vmname -Name "Snapshot Name" -Description "Snapshot Description" -Memory -Quiesce

Delete a Snapshot Using PowerCLI

To delete a snapshot of a virtual machine, you can use the Get-Snapshot cmdlet to list the snapshots for the virtual machine and then use the Remove-Snapshot cmdlet to delete the desired snapshot. Here is an example of how to delete a snapshot using PowerCLI:

  1. Use the Get-VM cmdlet to retrieve the virtual machine that has the snapshot you want to delete:
$vm = Get-VM -Name myvm
  1. Use the Get-Snapshot cmdlet to list the snapshots for the virtual machine:
Get-Snapshot -VM $vm
  1. Identify the snapshot you want to delete and use the Remove-Snapshot cmdlet to delete it:
$snapshot = Get-Snapshot -VM $vm -Name "Snapshot Name"
Remove-Snapshot -Snapshot $snapshot

Reverting a Snapshot

To revert a snapshot using PowerCLI:

  1. Use the Set-VM cmdlet to revert to it:
Set-VM -Snapshot "SnapshotName" 

NOTE: Keep in mind that reverting to a snapshot will discard any changes made to the virtual machine since the snapshot was taken.

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