Hi Lars,
"I shall not hijack/resurrect other threads!!" 
Thanks for answering btw ;-)
Yup, i've went thru those FAQ, admin guide, training guide and etc several times but still greasing my elbow to get the answer:
I did a comparison with other HANA system, as you can see, the Disk Size in first row was 40GB smaller compare to the backup size and used data volume size; whereas , value of other systems are pretty close.
Any clue what causing this that savepoint is write and updated to the used data volume (M_CONVERTER_STATISTICS) but not disk size (M_TABLE_PERSISTENCE_STATISTICS) that caused such a hugh difference?
What other info that persisted in memory and eventually to data volume but not to global disk?
Fyi, below are running fine:
i) delta merge
ii) savepoint
iii) mvcc
iv) total RS+CS tables is 2++ greater than M_TABLE_PERSISTENCE_STATISTICS. (which is true as this apply to other systems)
v) temporary table is small in size.
vi) couldn't find any note relate to this bug runing on 85.02.
Thanks,
Nicholas chang