Hi Praveen,
The modes supported by a given Agent Instance (through the underlying Source system Agent and the source that it connects to) is source-specific.
Each PCo Agent knows what type of read/write connectivity is supported for the source to which it is connected, and that list of connectivity features is presented to MII when you are configuring a PCoQuery template. if TagStore mode is not offered in the PCoQuery template as a mode, then interface to the underlying source does not support that type of mode.
Here is the current list of Historian Source agents and supported TagStore Modes, for PCo 15.0:
Vendor TagStore TagHistoryStore
OSiSoft PI yes yes
AspenTech IP21 yes yes
Proficy yes yes
CiTech SCADA yes no
OPCHDA yes yes
OPC-UA yes no
Regards, Steve