How to create, manage, and restore snapshots in VMware

In the fast-paced world of systems administration, having reliable mechanisms to protect the state of the Virtual machines, testing updates or recovering systems after errors is crucial. snapshots or snapshots in VMware They have become an essential tool for administrators and technicians, allowing them to work more securely in the face of major changes to servers and applications.

Although this is a powerful feature, there are many questions and myths surrounding its use, advantages, limitations, and proper management. Therefore, in this comprehensive guide, you'll discover everything essential (and a few tricks) for managing snapshots in VMware, from the basics, the files involved, the precise steps for creating and reverting snapshots, to advanced guidelines for avoiding performance and storage issues.

What exactly is a snapshot in VMware?

But what is a community? A snapshot It is essentially a point-in-time image of a virtual machine (VM), capturing its complete state at a given instant: including the contents of the virtual disks, memory (if chosen), and the machine's configuration. It works as a digitalized "photo" of the VM, saving the exact point to which you can return if any setback arises while making changes, testing patches, updates, or developing the system.

However, it should be clear that it is not equivalent to a traditional backup. A snapshot relies on the original disks and is meant to enable a quick and efficient rollback, but if the primary VM is lost, the snapshot alone won't be enough to recover everything. Therefore, Snapshots are complementary tools but should never be confused with or replace conventional backups..

What are snapshots used for in VMware?

The main purpose of snapshots is create quick restore points before operations that involve a certain level of riskTypical examples where they are vital:

• Before installing critical operating system updates or apply patches to applications.
• Prior to deep configuration modifications or installation of new system software or drivers.
• During testing or development processes, allowing you to “break” the machine and then undo the changes immediately and effortlessly.
• As temporary support for processes of backup at the host level, as some solutions use snapshots to ensure data consistency.

However, They are not intended to be used as definitive backups or to be kept active indefinitely.Having too many or old snapshots is a recipe for disaster: it can lead to bottlenecks, space issues, and the risk of data corruption.

How do snapshots work and what files are involved?

When you take a snapshot in VMware, A whole series of files and internal mechanisms are created to "freeze" the state of the VM:

• Delta files (-delta.vmdk or -00000x.vmdk): A differential disk is generated for each snapshot. These files record all subsequent changes made to the disk since the snapshot was taken. Each delta acts as a "change log" relative to the base disk and can never be larger than the original file (although it can come close in extreme situations).
• .vmsd: This file stores metadata and management information about all snapshots associated with the VM. It includes references, names, unique identifiers, and the relationships between snapshots and parent and child disks.
• .vmsn: This is the virtual machine's state file at the time of the snapshot. If you choose to save the VM's memory, this file will contain a RAM dump plus a few additional megabytes. Otherwise, its size will be reduced.
• Temporary files: During snapshot deletion or consolidation, additional delta files may also appear to complete the merging of recorded changes.

All these files, By default, they reside in the same directory as the virtual machine, although it is possible to relocate them manually by editing the configuration if there are special performance needs or storage.

How much space do snapshot files take up and how do they grow?

El The space required by a snapshot depends directly on the activity of the virtual machine. after their creation. Delta files start out small (usually 16 MB), but as disk writes occur, they grow in blocks. If you're working with servers that perform a lot of write operations (such as databases SQL, Exchange, etc.), delta files can quickly grow to a considerable size.

The maximum size of a snapshot will never exceed that of the original disk.For example, if you change absolutely every block on the disk after taking the snapshot, the delta file will be equal to the size of the base file, plus a small technical overhead.

Eye: The VMFS file system imposes size limits on virtual disks. If the sum of disk and snapshot overhead exceeds these limits, creating new snapshots may fail. It's important to consider these limits when defining the size of your virtual disks if you plan to use snapshots frequently.

Key differences between snapshots and backups

Although for many novice administrators it may seem the same, Snapshots serve a very different function than backups.:

• Snapshots: They are completely dependent on the original virtual machine files. They do not contain an independent, complete copy of all data; they simply store the differences since the last "freeze point." If the base disks are deleted, snapshots cannot recover the VM.
• Backups: They are independent copies, stored separately, and can reconstruct the entire virtual machine even if the original file is lost. They offer true data protection and disaster recovery.

Never use snapshots as a primary security mechanism for critical data or production systems.

Recommended use cases and warnings

Using snapshots It is especially recommended for development, testing and laboratory environments. There, the ability to quickly return to a previous state is essential and saves countless hours of work in the event of unexpected failures.

However, In production environments it is NOT recommended to have active snapshots for long periods.If a snapshot is created in a production environment for specific needs, it should be deleted as soon as possible to avoid performance degradation, space issues, and potential disk or memory inconsistencies.

Furthermore, Long chains of snapshots can cause real headaches.: The more points are chained, the more expensive it is for the storage system to reconstruct the VM state, since it must query all deltas sequentially before accessing the base disk.

What types of files make up a snapshot?

We have already seen some, but it is worth reviewing and delving deeper into each one:

• .vmdk (base disk): Master disk file of the virtual machine.
• –00000x.vmdk (disk delta or redo log): Record of all changes after the snapshot is created. For each new snapshot, another file of this type is added. When deleted, the changes are merged back to the parent disk.
• .vmsd: Metadata database for that VM's snapshots. It grows each time a new snapshot is created and stores the relationships between parent and child snapshots.
• .vmsn: Exact running state of the VM at the time of the snapshot (optionally including a full RAM dump).

When all snapshots are deleted, the delta files are integrated into the base disk and the entire auxiliary file structure is automatically erased.

How to create a snapshot in VMware step by step

Follow this process to create snapshots from the management client (vSphere Client HTML5 versions 6.5, 6.7, 7.0, and higher):

1. Right-click on the virtual machine you want to create a snapshot of. and select “Snapshots > Take Snapshot.”
2. In the dialog that opens, assign a name and description. Add enough information to identify the purpose and context of the snapshot, making it easier for you to manage it later.
3. Decide whether include VM memoryIf the virtual machine is powered on and you choose to save memory, the snapshot will include the machine's live state, allowing you to revert to that exact point (processes, services, etc.). If you don't select this option, the snapshot will restore the data, but the VM will boot afterward while powered off.
4. If applicable, select the option quiesce to ensure data consistency (very important on servers that are writing critical data to disk).
5. Click on CreateThe snapshot task will appear in the recent activities panel.

Tip: Although you can create a snapshot with the VM powered on, doing so with the machine powered off ensures greater consistency and reduces potential errors.

Managing and restoring snapshots

After creating a snapshot, you can view, edit, delete, or restore any saved points through the Snapshot Manager or from the VM's context menu:

• Revert: Returns the virtual machine to the exact state it was in when that snapshot was created.
• Edit: Allows you to modify the name and description.
• Eliminate: Deletes the selected snapshot, merging the changes to the parent disk.
• Delete all: Deletes all active snapshots, consolidating all changes to the original disk.

When you delete a snapshot, the system merges the changes from the delta files to the main disk. Weather required to complete this task depends on the volume of data modified since the last snapshot.

If you choose revert to a snapshot that doesn't include memory, the VM will revert to its previous state, but cold-booted (powered off). If the snapshot does preserve RAM, the machine will appear exactly as it was at the time of the capture, including running processes, services, and open windows.

Automating Snapshots with the Command Line and PowerCLI

In addition to the graphical interface, It is possible to create and manage snapshots using commands in console or scriptsThis allows you to automate recurring tasks, integrate them into other processes, or manage environments with multiple machines.

Some common syntaxes:

• To create a snapshot using PowerCLI:
  get-vm NOMBRE_VM | new-snapshot -Memory -quiesce -name "Nombre de la snapshot"
• To delete a snapshot saving your identifier in a variable:
  Remove-Snapshot -Snapshot $snap -RemoveChildren
• To revert to a snapshot specific:
  get-vm "NOMBRE_VM" | set-vm -snapshot "Nombre de la snapshot" -confirm:$false

If you prefer to use native commands in the ESXi console or vSphere CLI:
vmware-cmd nombre.vmx createsnapshot nombre 'descripción' 1 1
The last 1 indicates whether you want to freeze the VM's memory, and the second to last 1 indicates whether you want to quiesce.

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Windows Sandbox (WSB): The Ultimate Guide to Using Windows Sandbox

Isaac

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