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, 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. The data included in a backup unit (backup item) can be SSTable metadata, tablet metadata, or macroblock objects. By default, 2,048 backup units (each not larger than 2 MB) are aggregated into a file. You can modify the backup_data_file_size tenant-level parameter to specify the number of backup units aggregated into a file. Note that the sizes of metadata and macroblocks can be different, resulting in differently sized aggregated files.