RMAN backup size - v$rman_backup_job_details

Oracle 11.2.0.3

OS: Linux

I ran a LVL0 backup to tape,

Command:

BACKUP incremental level 0 as BACKUPSET tag '${RMAN_TAG_LVL0}' database; (note: I did not add plus archive logs)

Question:

What should I be expecting in Input and Output Bytes in v$rman_backup_job_details TABLE?

in the v$rman_backup_job_details table, Input Bytes column shows 102 TB and output_bytes shows 87.79. I was expecting the Input bytes close to sum(bytes) from DBA_Segments.

Total sum(bytes) from DBA_SEGMENTS = 78.18 TB(which shows all used bytes).

Thanks.