Backup and restore types

As of version 1.7.0, Percona Backup for MongoDB supports physical and logical backups and restores. This document describes each type.

Important

Physical backups and restores is the technical preview feature [1]. Before using them in production, we recommend that you test restoring from physical backups in your environment, and also use an alternative backup method for redundancy.

Physical backup is copying of physical files from the Percona Server for MongoDB dbPath data directory to the remote backup storage. These files include data files, journal, index files, etc. Physical restore is the reverse process: pbm-agents shut down the mongod nodes, clean up the dbPath data directory and copy the physical files from the storage to it.

During physical backups and restores, pbm-agents don’t connect to the database and don’t read the data. This significantly reduces the backup / restore time compared to logical ones and is the recommended backup method for big (multi-terabyte) databases.

Physical backups and restores are available for Percona Server for MongoDB starting from versions 4.2.15-16, 4.4.6-8, 5.0 and higher. Since physical backups heavily rely on the WiredTiger $backupCursor functionality, they are available only for WiredTiger storage engine.

See also

Percona Blog:

• Physical Backup Support in Percona Backup for MongoDB

• $backupCursorExtend in Percona Server for MongoDB

Logical backup is the copying of the actual database data. A pbm-agent connects to the database, retrieves the data and writes it to the remote backup storage. During the restore, the reverse process occurs: the pbm-agent retrieves the backup data from the storage and inserts it to the dbPath data directory.

Logical backups allow for point in time recovery

Type	Advantages	Disadvantages
Physical	Faster backup and restore speed Recommended for big, multi-terabyte datasets No database overhead	The backup size is bigger than for logical backups due to data fragmentation extra cost of keeping data and indexes in appropriate data structures Extra manual operations are required after the restore Point in time recovery is not supported
Logical	Easy to operate with, using a single command Support for incremental backups and point-in-time recovery The backup size is smaller as it includes only the data	Much slower than physical backup / restore Adds database overhead on reading and inserting the data

[1]

Tech Preview Features are not yet ready for enterprise use and are not included in support via SLA. They are included in this release so that users can provide feedback prior to the full release of the feature in a future GA release (or removal of the feature if it is deemed not useful). This functionality can change (APIs, CLIs, etc.) from tech preview to GA.