If data checksums are enabled in the database cluster, pg_probackup3 uses this information to check correctness of data files during backup. While reading each page, pg_probackup3 checks whether the calculated checksum coincides with the checksum stored in the page header. This guarantees that the Postgres Pro instance and the backup itself have no corrupt pages. Note that pg_probackup3 reads database files directly from the filesystem, so under heavy write load during backup it can show false-positive checksum mismatches because of partial writes. If a page checksum mismatch occurs, the page is re-read and checksum comparison is repeated.

A page is considered corrupt if checksum comparison has failed more than 300 times. In this case, the backup is aborted.

Even if data checksums are not enabled, pg_probackup3 always performs sanity checks for page headers.