As we know with Microsoft SQL Server everything is processed from disk and loaded into the buffer pool for processing by the query engine. So what happens to the buffer pool when backups are taken?
The answer is that nothing happens to the buffer pool.
When SQL Server is backing up data from the disk, SQL Server simply takes the data from the data files and writes it to the backup file. During the backup process the dirty pages are written to the disk by the checkpoint process being triggered by the backup database process.
Because the backup process simply reads the data files and writes them to the backup location there’s no need to cache the data in the buffer pool as this data isn’t being queried by a normal SQL query.