In this blog we will talk about what is quiescing in VMware vSphere for Virtual Machines, and how BDRSuite can help us to quiesce a virtual machine before taking the snapshot, for Application Consistency. But before we dive into what quiescing is, let’s understand what snapshots are.
What are Snapshots?
Snapshots help in preserving the state (VM Power State) and data (Files) of a virtual machine at a specific point in time. Snapshots come in handy when any changes that occur on the Virtual machines go wrong. With VMware vSphere, when we create VM snapshots we provide the name, description, include / exclude memory state of the VM and enable / disable quiesce. Depending upon the options we select for VM Snapshots, it takes time accordingly.
For example when we include the memory state of the VM,a dump of the internal state of the virtual machine is included in the snapshot and may take longer, however this is beneficial in case when we have to reverse to the running VM state at a later point of time.
When a snapshot is created, there are various files which are created
- -.vmdk and –delta.vmdk – Child Disks or Delta Disks
- .vmsd – Database for keeping Virtual Machine Snapshot Information
- Snapshot.vmsn – current configuration and the active state of the VM
What is Quiescing ?
Quiescing the Virtual Machine is a process of bringing the on-disk data into a state which is suitable for backups. Quiescing pauses the state of running processes on a machine, to guarantee a consistent and usable backup.The quiescing operations of a VM ensures that a snapshot represents a consistent view of guest file system state at a specific point in time. Quiescing operation will work when the VMware Tools are installed in the Virtual Machine.
The Quiescing process is important when there is a need for backup since the backup data should be in a consistent state and can also be used during recovery.
BDRSuite Guest VM Processing
While Configuring the Backup, BDRSuite (VM Backup) uses the quiesce method of snapshot to backup the Virtual Machines and make sure the backup data is recoverable and crash consistent during recovery. Quiescing and enabling Guest VM Processing can be combined together to achieve higher consistency during the backup Operation.
Guest Processing Settings is an optional step, we can also continue without setting up the guest processing. If the guest OS processing is not enabled, the snapshot is taken irrespective of whether the VSS Writers are stable or not.
BDRSuite further provides the option to use Application Aware Processing for application consistency of Microsoft applications such as Microsoft Exchange Server, MS SQL Server, Active Directory, MS SharePoint, and Oracle database inside the VM.
- On selecting Require successful application processing (recommended), the backup will continue only if all the application writers are stable and the application-aware processing is successful
- On selecting Ignore application processing failures (Not Recommended), the backup will proceed regardless of whether application-aware is successful or not
- On selecting Disable application-aware processing, the backup will proceed without ensuring the transaction consistency for the applications inside the VMs
Note:We need to Provide the credentials of the VM to perform the Guest OS Processing
After Configuring the Guest Processing Settings and entering the Guest Credentials, BDRSuite Backup Server GUI provides us the direct option to Enable VMware Quiescing, so as the Virtual machines are quiesced before the snapshot operation and a better application consistency can be achieved during the backup operation.
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