So, let me try to explain the problem again.
6.11.5:
ZFS(RAIDZ1) with zpool called zfs.
User share e.g. downloads with a link data to a dataset called downloads in the zpool called zfs
Upgrade to 6.12.4
6.12.4:
Create a new pool - zdata, and add all HDDs.
Global Share Settings -> Permit exclusive shares.
Change primary storage for downloads to zfs pool zdata.
Now, since the exclusive access is shown as NO
renamed old share to downloads_old.
created new share called downloads with primary storage as zdata.
move data from downloads_old to downloads.
Remove old share downloads_old.
^^^^^^^^^^ This is when I lost data ^^^^^^^^^^^^^^
NOTE: Before trying on downloads, I had tried with other shares.
After this disaster, I left my last share as is to avoid more data loss. This is the share which you see as exclusive access marked as NO.
I had TWO issues,
a) Loss of data and
b) How to enable exclusive access without going through arduous process creating a new share and copying close 3 TB of data.