The OP has nothing to do with backups. fsync(2) and friends are also necessary to ensure correct ordering of writes to disk, which in some ways is more importa

The OP has nothing to do with backups. fsync(2) and friends are also necessary to ensure correct ordering of writes to disk, which in some ways is more important than ensuring that the data is actually committed. If certain writes aren't written in the order expected, then applications lose crash consistency and now you have corrupt data, not just missing data.