In simple terminology, we know that a virtual machine exists in an abstract form of files. The snapshot feature takes advantage of this and leverages file manipulation techniques to capture the current state in one set of files while a newer state (or delta from the present state) is redirected to a newer set of files. It does it in the following sequence of steps:
- If the virtual machine memory is included, the ESXi host flushes the memory of the virtual machine to disk (*.vmem)
- If the Quiesce guest file system (Need VMware Tools Installed) option is selected, the host invokes quiescing through the VMware tools.
- File state changes are written to a *.vmsd file such that the snapshot manager UI populates the snapshot chain.
- Any new writes are redirected to the snapshot disks created (*-0000X.vmdk and *-0000X-sesparse.vmdk).
The following screenshot is obtained through SSH access to the ESXi host, where the virtual machine currently runs. Note the files created and modified in the timestamp Aug 21 15:19, this reflects the effect of a typical snapshot operation:
