Back in old days, upgrading an OS running on physical servers or upgrading any application used to be a tedious job. Administrators had to ensure that they have a valid backup available for their physical servers before they could proceed with the application or OS upgrade. In unfortunate situation of any failure, the only option available was to restore the server from the good backup. Restore is not even guaranteed recovery as the backup file vulnerable to corruption.
With VMware Snapshots everything has changed drastically. Almost all the people who are into virtualization are familiar with the term 'Snapshot'. This is a term that was popularized by VMware environments and is one of the most useful feature in the virtual environment.
A snapshot preserves the state and data of a virtual machine at a specific point in time.
The state includes the virtual machine’s power state (for example, powered-on, powered-off, suspended).
The data includes all of the files that make up the virtual machine. This includes disks, memory, and other devices, such as virtual network interface cards.
In simple words, snapshots simplifies the process to capture the Point-in-time copy of the virtual machine without the need of any third party backup software. You can take multiple snapshots to preserve the multiple states of the virtual machine. It also simplifies the restore process. If something goes wrong to the VM(eg. during OS/Application Upgrade), you can go back to that point before it occurred.
Snapshots are generally used for development and testing purposes. Mistakenly, some people still consider snapshots as a backup because it allows a VM to return to a previous state. However it's important to note that snapshots should not be considered as a backup. Running a virtual machine on a snapshot for extended periods of time can cause performance issues, instability and data loss.
How to create a snapshot?
1. Login to the vCenter using vSphere Client (HTML5)
2. Select a VM on which you want to take a snapshot. Click on ACTIONS > Snapshots
3. In the snapshot wizard, provide the snapshot a Name and Description
Depending on your requirement, you can choose either snapshot with VM memory or Quiesce
Snapshot the virtual machine’s memory
This option is enabled by default. When you create a memory snapshot a dump of the internal state of the virtual machine is included in the snapshot. Memory snapshots usually take longer to create, but allow reversion to a running virtual machine state as it was when the snapshot was taken. If memory snapshot and quiescing both the options are not selected, the snapshot will create files which are crash-consistent, meaning you’ll need to power up the VM manually after having it restored from snapshot. It's important to note that while taking a memory snapshot, the entire state of the virtual machine will be stunned.
Quiesce Guest File System
This option requires that VMware Tools are installed and running. If you select this option and the virtual machine is powered on when the snapshot is taken, VMware Tools is used to quiesce the file system in the virtual machine.
Quiescing a file system is a process of bringing the on-disk data of a physical or virtual computer into a state suitable for backups. This includes operations such as flushing dirty buffers from the OS’s in-memory cache to disk or other higher-level application-specific tasks. Quiescing indicates pausing or altering the state of running processes on a computer, particularly those that might modify information stored on disk during a backup, to guarantee a consistent and usable backup.
Quiescing snapshot is used primarily for backups.
4. Click on OK after selecting appropriate option.
That's it for now. In the next posts we will discuss more about snapshot files and how to manage snapshots.
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Thank you for reading!
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