How to implement snapshot and incremental backup of OpenStack virtual machine

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1 the concept of snapshot

The general understanding of snapshots is to be able to restore the system to a certain moment, which is what snapshots do.

Snapshot is divided into memory snapshot and disk snapshot according to the data to be saved, memory snapshot is to save the data of current memory, and disk snapshot is to save the data of hard disk.

Snapshots are divided into internal snapshots and external snapshots according to the way they are saved.

Internal snapshot: refers to the snapshot information and the virtual machine in the same qcow2 image, using a single qcow2 file to save the snapshot and the changes after the snapshot. This snapshot is the default behavior of libvirt and is now well supported (create, rollback, and delete), but only for disk mirror files in qcow2 format, and the process is slow, and so on.

External snapshot: it means that when taking a snapshot, the disk of the original virtual machine will become the template image of readonly, and then a new qcow2 file will be created to record the difference data between the original template image and the original template image. The result of the external snapshot is to form a chain of qcow2 files: original