I wanted to store all the data from my DB to dstore so, What is maximum number of data or size can be stored in Dojo dstore?
This is a very vague question, since you don't even mention what type of store specifically. With in-memory stores it's usually advisable to keep totals down to a couple of thousand, though modern browsers can certainly scale higher.
However, the entire point of server-based stores like Request and Rest are that not all items need to be stored on the client side at once. If you have hundreds of thousands of data items and your server providing the data supports filtering/sorting/paging arguments in some way, whether restful in the way that Request and Rest expect or otherwise, a server-based store (i.e., one that queries the server for each fetch or fetchRange call, passing arguments based on any preceding sort and filter calls) is a good idea.
You can get an idea for the kinds of server interactions that the Rest store expects here (although this documentation was written for implementations of older store APIs, dstore/Request and dstore/Rest still expect the same type of behavior, but are slightly more configurable).
You can also see an example of configuring and using dstore/Rest with one particular server-side framework, the Django Rest Framework, here.