[PVE-User] pve-zsync + borgbackup "changed size" discrepancy

[devzero at web.de]

hi,
i'm syncing a zfs dataset with pve-zsync to another proxmox host and also do backup with borg-backup of the same
dataset via temporary backup snapshot.

i have shutdown all VMs on the dataset and only leave a single win10 vm up and running.

i see a huge discrepancy between what pve-zsync is reporting as "changed data" to be synced to the other node
and what borbackup is reporting regarding backup growth (see below). ("deduplicated size" means: this is the size
the archive grew after the data has been checksummed, deduplicated and compressed)

does anybody have a clue why this differs by "roughly a power of 10" ?

is pve-zsync estimation wrong ?
is borgbackup "overhead" so big when backing up large single qcow2 files ?

regards
roland

pve-zsync estimated size:
total estimated size is 1.79M
total estimated size is 22.9M
total estimated size is 13.5M
total estimated size is 24.4M
total estimated size is 22.9M
total estimated size is 24.1M
total estimated size is 10.2M
total estimated size is 20.9M
total estimated size is 81.0M
total estimated size is 53.3M
total estimated size is 10.8M
total estimated size is 14.1M
total estimated size is 10.9M
total estimated size is 189M
total estimated size is 29.0M
total estimated size is 21.2M
total estimated size is 14.1M
total estimated size is 13.1M
total estimated size is 11.0M
total estimated size is 14.1M
total estimated size is 11.3M
total estimated size is 14.9M
total estimated size is 10.5M
total estimated size is 14.2M
total estimated size is 20.4M

BorgBackup growth
                       Original size      Compressed size    Deduplicated size
This archive:              111.69 GB             19.86 GB             95.31 MB
This archive:              111.69 GB             19.86 GB            197.58 MB
This archive:              111.69 GB             19.86 GB            119.40 MB
This archive:              111.69 GB             19.86 GB            138.81 MB
This archive:              111.69 GB             19.86 GB            180.30 MB
This archive:              111.69 GB             19.86 GB            205.75 MB
This archive:              111.69 GB             19.86 GB             76.22 MB
This archive:              111.69 GB             19.86 GB            159.60 MB
This archive:              111.69 GB             19.86 GB            636.18 MB
This archive:              111.69 GB             19.86 GB            413.14 MB
This archive:              111.69 GB             19.86 GB             83.86 MB
This archive:              111.69 GB             19.86 GB            122.86 MB
This archive:              111.69 GB             19.86 GB            108.17 MB
This archive:              111.69 GB             19.86 GB            153.89 MB
This archive:              111.69 GB             19.89 GB            946.72 MB
This archive:              111.69 GB             19.89 GB            126.48 MB
This archive:              111.69 GB             19.89 GB            139.23 MB
This archive:              111.69 GB             19.89 GB            113.23 MB
This archive:              111.69 GB             19.89 GB             67.53 MB
This archive:              111.69 GB             19.89 GB            129.25 MB
This archive:              111.69 GB             19.89 GB             74.28 MB
This archive:              111.69 GB             19.89 GB            110.28 MB
This archive:              111.69 GB             19.89 GB             80.15 MB
This archive:              111.69 GB             19.89 GB             92.86 MB
This archive:              111.69 GB             19.89 GB            160.57 MB