The read and write “total bytes” are the same when there is no compression or deduplication occurring.
When compression or deduplication is being used, the total bytes read should be higher than total bytes written, since compression reduces the write volume.
The read volume is less than the total of all original files because some were skipped. This happens after the first full backup.
Files are skipped when their last write access time stamp matches between original and backed up file, which is interpreted as an unchanged file and BackupChain skips it.
Skipped files aren’t counted in the ‘total bytes read’ statistic.