HBS Sync very slow TS-1673-RP

[Hemant_5400z]

Hi All,

I have A TS-1673-RP running QTS 5.2.4.3079 (latest version).
I'm trying to backup my Data from QNAP to Synology (DSM 7.1). Unfortyunately cannot use HBS normal so stcuk with SBM or rsync. (one way sync)

Issue is as follwos When i do an initial backup from QNAP to synology around 500 GB data the job finished with 2 hours all data on my synology. However when i do the next backup so second time same folder it takes 3-4 hours while nothing changed on files but sync takes ages.

I tried on BTRFS volume also on EXt4 but same issue very slow, this is a test setup before i do the whole NAS but whit this speed this is useless.
I'm not sure what it is actually doing, also when I stop the job on qnap, looks like it is still running on the background as i can see rsync still active on the backgroudn which is weird. When i reboot Qnap the connection on syno finally goes away.

The sync job 2nd time should take minutes, because it started right after initial sync finished.

Any help appreciated, i would like to make regular full backups of my qnap.

Cheers,
Hemant