Slow incremental backup

When I do incremental or differential partition backup (v., it takes very long to complete every time i run it (about 1 hour, partition has about 50GB data). Is it supposed to be that slow or am i doing something wrong?

The steps that run too long is “Determining changes since last backup”

Interesting thing is that when i make incremental FILES based backup from the same partition and selecting whole C drive, it takes less than 5 minutes.

Backup file is located in network (100Mbit) and with file based backup, there is almost no traffic but partition based is writing/reading over network the whole time.

The difference between files versus partition (sector-by-sector) backup is that for files the time stamp is used to determine if something has changed, but for partitions the entire partition must be read again to determine the changed sectors. There is no time stamp for sectors.