SharePoint backup process

DPM coordinates the backup across multiple servers in the farm to back up data. After backup is done, DPM queries the SharePoint object model and gets all the information about the site and items from the SharePoint server. SharePoint protection uses the SharePoint VSS writer to protect the entire farm. SharePoint VSS writer is a referential writer, and DPM uses the SharePoint VSS writer to obtain the SharePoint topology, such as the SharePoint content databases and the configuration database that are part of the SharePoint farm. With this information, the SQL Server configuration and content databases are backed up.

As far as SQL Server backup is concerned, it uses exactly the same workflow as backing up SQL Server databases as discussed in the previous section. The data movement for the SQL Server databases happen from the SQL Server machine to the DPM replica server directly, and the SharePoint front-end server and the VSS writer are not involved. Each content database is backed up independently since there is no referential integrity or consistency requirements across the database in a SharePoint farm.

For example, assume the SharePoint farm contains contentDB1, contentDB2, and configDB on SQL1 instance and contentDB3 and contentDB4 on SQL2 instance. SQL1 instance databases contentDB1.mdf, contentDB1.ldf, contentDB2.mdf, contentDB2.ldf, and configDB.mdf are backed up directly from SQL Server SQL1 machine, whereas contentDB3.mdf, contentDB3.ldf, contentDB4.mdf, and contentDB4.ldf are backed up directly from the SQL Server SQL2 machine. It is critical to note that although SQL backup is taken by the SQL VSS writer, transaction log backup is done as part of SharePoint SQL server backup.

SharePoint supports partial backup. Since SharePoint farms can be large, failure to back up
a single database in the farm doesn’t result in complete farm backup failure. Backups for one or more databases can fail, but a recovery point is created with all other databases. Similarly,
when a new content database is added, its initial replica is seeded to the DPM replica server
through a nightly job. To immediately add a content database to the protection group, you
can add it manually.

Source of Information : Microsoft System Center