Linux in a Nutshell, 6th Edition

Snapshots

ESX can take snapshots of a running system. This process essentially freezes machine state and begins tracking changes to the system in a separate file. Later you can apply those changes or discard them to revert your system to the state it had when you took the snapshot. This is commonly used to test a configuration change or system update.

Because it preserves a system’s state at a specific time, you want your virtual machine doing as little as possible when taking the snapshot. Activity such as network file transfers and database transactions will fail if you decide to revert to the snapshot. Depending on virtual machine configuration, some disk activity may not be included in the snapshot.

The file tracking changes can grow quickly, so you will need sufficient space to hold the file, and you will probably not want to keep snapshots for very long. Having a snapshot may also limit your ability to migrate a system between servers.

Restoring the snapshot on a new system may not work. VMware will generate warnings when you try to migrate a system with a snapshot. Generally you want to remove all snapshots before migration.