[CentOS] [rsync -avz] total size/disk usage difference between source and destination

Hi folks

We migrated storage from local disk to SAN with:

# rsync -avz /mnt/lvol00045/* /lvol00045

Why there is a difference in size? How to explain this? Do we have
inconsistency? What we did wrong?

[...]
/dev/mapper/vg01-lvol00045_old
                      10321208   3930336   6286016  39% /mnt/lvol00045
[...]
/dev/mapper/vg01-lvol00045
                      10321208   3163852   6633068  33% /lvol00045
[...]

kind regards
Sven