This topic describes the architecture and storage mechanism of data backup.
Data backup architecture
Data backup preferentially uses a follower replica for backup. The data backup architecture is shown in the following figure.
Storage mechanism of data backup files
The native NFS protocol performs poorly when it handles a large number of small files (for example, tens of millions of 2 MB files). To address this issue, OceanBase Database introduced data aggregation storage in V4.x. Specifically, data backup files are packaged and stored in batches to reduce the number of small files. A backup item is a unit of data that can be packaged and stored. It includes the metadata of SSTables, tablet metadata, and macroblocks. By default, 2,048 backup items (each not larger than 2 MB) are aggregated into a file.
Note that the sizes of the metadata and macroblocks can vary, resulting in files of different sizes after aggregation.