Question

Snapshots in VMWARE

Answer 1

Introduction

A snapshot is a capture, as if it were a photo, of a virtual machine with its data and devices ..
After creating the snapshot and continuing to work with the Virtual Machine it is possible to return to a previous state of the same by recovering any of the snapshots.

VMware vSphere allows you to create up to 32 snapshots per Virtual Machine although it is not recommended to use more than 2 or 3 simultaneously. It is not even recommended to use virtual machines in production with active snapshots.


: Let's clarify that :

" SNAPSHOTS CAN NOT BE CONSIDERED AS A BACKUP OPTION" .

A Virtual Machine with snapshots degraded its performance by having its data fragmented into different disks and forcing the " Host" to devote more resources.
And also, when generating each Snapshot, we are creating a dependency between the different files of Parent and Child discs.

Creating a Snapshot

Options when creating a snapshot, as we see in the image, when we create a snapshot of a VM on, we have two options.

Snapshot the virtual machine's memory; captures the state of the Virtual Machine's memory. If we do not mark this option when we create the snapshot, at the moment of recovering it, the VM will be turned off.

Quiesce guest file System; this option allows us to generate the snapshot with the state of the disk in consistent mode. This means that when you finish creating the snapshot, even if there were changes to the disk during the creation of the snapshot, at the end of the snapshot it includes both these changes and the operations that are in cache.
This option requires that the Virtual Machine have the VMware tools installed.

Manager

Go to; if we select a snapshot and click on " Go to" we will go to the state of the VM at the time and configuration in which the snapshot was taken.

Delete; selecting a snapshot and clicking " Delete" will eliminate the snapshot. It is not possible to recover a deleted snapshot, except with a BACKUP of the VM.

Delete All; by clicking on the " Delete All" button we will eliminate all the snapshots leaving a single virtual disk with the state of the last snapshot.

Consolidate: The Consolidate option is new from version 5 of vSphere. This option unifies the Parent disk and the Childs in a single disk. The new option C onsolidate solves problems of deleted snapshots that keep the files of Child discs in the Datastore occupying valuable disk space.

Snapshot files

When we visualize the files of the Virtual Machine from the vSphere GUI environment, we will only see the pointers to the disks but with the size of the delta files.
If we copy or move all the files will be transferred.

VMSD : It is the file that describes the snapshots of the Virtual Machine. It is created in the same folder of the Virtual Machine and only exists if there is at least one snapshot.
This file is the information source of the Snapshot Manager and defines the relationship between the Parent and the Child discs .

Image of a .VMSD file of a VM with 3 snapshots

VMSN: When you create a snapshot of a Virtual Machine on, optionally, it is possible (and highly recommended) to capture the state of the memory. For each snapshot that is created by capturing the state of the memory, a .VMSN file is created. Each .VMSN file is related to a snapshot that was created by capturing the state of the memory.

<name-vm> - <number> .VMDK and <name-vm> - <number> -delta.VMDK ; For each snapshot that we create in a Virtual Machine these two disk files will be generated. One is a pointer to the delta disk file and the other is the delta disk itself. The delta disks are differential disks of the main disk of the Virtual Machine (Parent disk). These discs are also called Child disks .

CID = 062F182a: 8-digit hexadecimal code identifying the disk
parentCID = 8d5e3a8e: Hexadecimal code of the Parent disk
parentFileNameHint = "W7 Demo.vmdk": Parent disk name and path
RW 67108864 VMFSSPARSE "W7 Demo-000001-delta.vmdk": Logical size of the snapshot and name of the disk.

Snapshots are an extremely useful feature but you have to know how to get the right match. If we do not manage them correctly, they can turn against us.

---