Hello Raj,
thanks for your interest in BaseX.
You can see the current upper limits of Basex at [1]. As you can see, the current upper file size limit is 512GiB per database. However, you can always distribute your data across several databases as databases in BaseX are a fairly lightweight concept and you can also access multiple databases within one XQuery expression. So, theoretically you can save Terabytes of data.
However, if query execution against such a large database will be efficient is very difficult to tell. It heavily depends on the type of query you want to run, but personally I would not expect a blasting performance. But again, this is very hard to tell.
Scaling out and replication is currently not supported by BaseX. Of course you can always use some kind of distributed file system to physically distribute your data, but BaseX itself is not doing this for you. Of course, you could start several BaseX servers and store certain data at specific servers, but there will be no synchronization of any kind. However, we would love to change this and this is actually my current project.
I gave a short talk about our plans at our user meet-up at XML Prague. You can see the slides at [2] (hopefully the videos will be there as well any time soon). So, we are interested in scaling out and replication. Therefore, I am also very interested in real-world use cases. I would be very interested if you could tell me more about your specific requirements (either by private mail or mailing list), so that we in the end will have a real-world usable solution.
Cheers,
Dirk