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What is Quiescing for VMware vSphere VMs?

Snapshots are used to capture relevant information about a virtual machine at specific times. Quiescing, on the other hand, refers to altering a running process to prevent a specific action. Snapshots and quiescing are not the same thing, but some PC users view them as one. In this article, we will explain quiescing for vSphere VMs.

VMware vSphere is widely recognized as the most popular and commonly used virtualization platform; it includes a vCenter Configuration Manager and a vCenter Application Discovery Manager. vSphere also utilizes vMotion for migrations from one host server to another—one VM at a time. Should you quiesce an ongoing process in vSphere? And how can you do it? Let's find out.

What is Quiescing?

For some, quiescing is essential when capturing snapshots in a virtual environment, while for others, it's merely an optional feature. Regardless of your stance, understanding what it means to quiesce in vSphere is crucial.

vSphere provides a range of tools and features that facilitate effective virtual machine management. It offers an intuitive virtualization environment that is accessible even to those new to virtualization. VMware regularly updates vSphere, adding new features and enhancing support for broader server and VM management capabilities.

On the vSphere platform, you can take snapshots of your virtual machines. These snapshots capture the state and data of your VMs at a specific moment, recording details like the VM's power status, memory, connections, and other pertinent information.

vSphere enables various snapshotting methods and options, allowing you to tailor your snapshots. It also supports the creation of snapshot chains or extensive snapshot trees. One notable feature is "Quiescing," which enables snapshots to be taken without interruption from ongoing activities.

Interruptions during snapshot creation can pose issues when attempting to revert to a previous state. To avoid this, some users prefer to take snapshots when the VM is idle, particularly when not undergoing heavy I/O operations. For instance, taking a snapshot during a file transfer might result in a corrupted file if you later revert to that snapshot. Essentially, any active processes during the snapshot will not be captured accurately.

To circumvent such issues, many opt for quiesced snapshots over memory snapshots. Quiesced snapshots, which are taken when a VM is forced into a stable state for backup, are generally faster to record than memory snapshots. This makes them preferable for ensuring data integrity during backup processes.

Learn more about VMware Snapshots best practices.

What is the Purpose of Quiescing?

Just one word – STABILIZATION. Yes, that’s the purpose of quiescing. Taking snapshots or making backups of a VM when there are multiple ongoing processes or transfers is as good as “nothing” because you won’t be able to use the snapshot – the files will be corrupted. Unless you only take snapshots when your VMs are idle, then quiescing is not what you may be interested in.

Quiescing guarantees data integrity and ensures you take “workable” snapshots you can rely on in times of crisis. It is advisable to run a quiesce backup before making critical changes to your VM or applying system updates. This is to enable you to have a place to fall back on if things don’t go as planned.

Snapshots in VMware vSphere

How Snapshot works in VMware? To some people, quiescing is a must when taking snapshots, and to others, it’s an optional setting. Whichever one you fall into, it is important to understand what it actually means to quiesce in vSphere.

Apparently, vSphere offers very useful tools and features for effective virtual machine management. It provides an intuitive virtualization environment that even novices can easily navigate and use. VMware releases new versions of vSphere to include newer features and extend support for more server and VM management functions.

You can take snapshots of your virtual machines deployed in VMware’s vSphere platform. These snapshots preserve the state and data of your virtual machine(s) at a specific point in time. Information recorded in a snapshot includes a VM’s power status, memory details, connections to the VM, and other useful information.

vSphere offers different snapshotting techniques and options to allow you to customize your snapshots and also record snapshot chains or create extensive snapshot trees. One of the snapshotting features offered by vSphere is “Quiescing,” a feature that lets you run snapshots without the process being interrupted by ongoing activities.

When a snapshot is interrupted due to ongoing processes on the VM, it becomes a problem when you want to revert to the snapshot. Some users prevent this by taking snapshots when the VM is idle and not running any intense I/O activities. For example, if you take a snapshot when a file is being transferred to another VM when you revert to the snapshot, that file will appear as corrupted. So to say, any running action during a snapshot will not recorded.

To avoid this, most people prefer to run quiesced snapshots rather than memory snapshots. Quiesced snapshots are recorded faster than memory snapshots. Quiesced snapshots are snapshots taken when a VM is forced into a stable state for backup (a snapshot).

The whole essence of snapshots in VMware vSphere is to record specific details of a VM at a given time. Snapshots are like “backups,” but not really backups. vSphere offers two main types of snapshots: Memory Snapshot and Quiesced Snapshot.

Memory State Snapshots vs Quiesced Snapshots

Both have the same primary purpose – to create a “restore point” for your VM and include specific details you may need while restoring the snapshot. What differs between these two vSphere snapshot types is how they perform their task. But memory snapshot is the default option in vSphere.

Memory snapshot captures a VM in its exact state without altering any ongoing process (if any). This type of snapshot, when restored, takes you back to the exact state of the VM at the time when the snapshot was captured; you will also see the state of running applications on your VM as of when the memory snapshot triggered.

On the flip side, a quiesced snapshot begs to differ. This snapshot will alter your VM’s state before a capture. If there is an ongoing process or running application, and a quiesced snapshot is triggered, first of all, the trigger will halt all ongoing activities, stabilize the VM, and then record a capture. So, this type of snapshot doesn’t tell or show the exact state of ongoing applications as of when it was recorded.

You can rely on a quiesced snapshot  as a backup copy since there will be no corrupt file when the snapshot is restored. But for memory snapshots, all running applications or file transfers may appear as a corrupt file (not in all cases). This summarizes the difference between these snapshot techniques supported in VMware’s vSphere environment.

One more thing, memory snapshots take more time to capture than quiesced snapshots; this is because the memory snapshot command relies on the memory size allocated to the VM to write the memory to disk. Hence, low memory space will lead to slower copy speeds. Both quiesced and memory snapshots record the same thing: the VM’s state, power settings, and applications’ status.

Learn more about EBS Snapshot AWS.

Creating a Quiesced Snapshot in vSphere

Quiesced snapshot is not the default snapshot selection in vSphere, so if you’d prefer this snapshot to a memory state snapshot, then you should know how to enable it on your vSphere environment. Firstly, you must have VMware Tools running on your virtual server. Once this is done, here is how vSphere will prepare your VM for a quiesced snapshot:

  • Using VMware Tools, the VMware Snapshot Provider function creates a new VSS (Volume Snapshot Service) snapshot in the guest operating system.
  • The VSS writers then prepare all active applications for the backup
  • Transactions get written from memory to disk.
  • The VSS reports to the VMware Tools Service that all prerequisite actions are completed.
  • Your system is now ready for a quiesced snapshot.

For vSphere 7.0 Users:

If you use vSphere 7.0, you can create quiesced snapshots from the vCenter interface. Simply follow the steps below:

  • Step One: Launch vCenter and select a VM you want to backup
  • Step Two: Right-click on the VM, and go to Snapshots 🡺 Take Snapshot.
  • Step Three: Look towards the bottom of the popup dialogue box and you will notice that Include virtual machine’s memory is checked by default (that’s the Memory-State Snapshot), uncheck it and select Quiesce guest file system.
  • Step Four: Click Create and a quiesce snapshot will be taken. To view the snapshot, go to the Snapshots tab, from there, you can revert, edit, or delete the snapshot.

How to Recover VMware Snapshot?

You can recover deleted snapshots using a third-party tool that supports the VMFS file system. The third-party tool will recover your snapshot’s vmdk file, and then you can restore it on vSphere. But if you didn’t delete the snapshot entirely – you just mistakenly deleted only the descriptor file, you can recover the deleted descriptor file by creating a new one and naming it just the same as the old (deleted one).

On vSphere Web Client

  • Launch the vSphere Web Client and go to the Storage tab
  • Click on Datastore and open the folder containing the VM data of which its snapshot’s descriptor file went missing or got deleted.
  • Download all files in this folder to a local folder
  • Once the download is done, look for .vmdk files and open them using Notepad (the essence of this is to locate the parent disk and file name of the deleted snapshot).
  • When you find the snapshot descriptor files, duplicate/copy one of them into a new notepad and rename it to bear the same name as the deleted one.
  • Now, change parentFileNameHint=" VMname.vmdk" to the actual parent disk name of the deleted snapshot. Also, change the values of RW 12582912 VMFSSPARSE "Windows Demo-00000#-delta.vmdk" with the file name of the deleted snapshot delta disk name.
  • Upload this newly created descriptor file to the VM folder of the VM with the missing snapshot descriptor file.
  • Power on the VM and you should be able to restore the snapshot.

Note: This only works when what is missing is the snapshot’s descriptor file. If the snapshot file itself has been deleted, you cannot recover it on vSphere, you need a third-party solution.

Using DiskInternals VMFS Recovery

This becomes the only choice if the snapshot files are missing entirely. A professional DiskInternals VMFS Recovery software can help you recover the lost files.

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  • Step One: Launch DiskInternals VMFS Recovery and your drive’s filesystem
  • Step Two: Choose a recovery mode – it is better to choose “Full Recovery” mode – and start the scan.
  • Step Three: Select a Power Search feature that suits your “time” and DiskInternals VMFS Recovery will launch a scan to recover your files.

Step Four: The recovered vmdk. files will be marked with an asterisk; identify, and save them to storage. But, you must have DiskInternals VMFS Recovery PRO version to save the recovered files.

What More?

Quiescing in vSphere is a snapshotting technique that stabilizes the VM first before recording a shot. It is best used for creating restore points for database VMs. Quiescing is not the default snapshot type on vSphere, so you have to select it manually. If peradventure your snapshot files go missing, you can recover them using the guide provided in this article.

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