hi,
Is there any way we couldn't find out how much data coming to an particular index ?
Here's a posted answer pretty close to what you need. http://answers.splunk.com/answers/154773/how-to-create-a-report-that-shows-max-indexed-volume-per-da...
Also, I noticed a useful search by sourcetype over on the Big Book of Splunk Searches. If your sourcetypes are unique by index, then that would work for you.
Try this below link and modify the query to alltime
https://answers.splunk.com/answers/242759/help-to-find-daily-indexed-data-size-by-each-index.html
I suggest that you use the Monitoring Console and look at the indexing dashboards.