# Need to test a index with terabytes of data, how can I do **URL:** \ **Category:** Elasticsearch\ **Tags:** rally\ **Created:** [May 12, 2021, 8:56am UTC](https://discuss.elastic.co/t/need-to-test-a-index-with-terabytes-of-data-how-can-i-do/272787 "2021-05-12T08:56:50Z")\ **Posts on this page:** 1\ **Showing post:** 8
**Author:** ![GITnewfish](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/gitnewfish/32/87303_2.png) [@GITnewfish](https://discuss.elastic.co/u/GITnewfish)\ **Post date:** [May 24, 2021, 8:30am UTC](https://discuss.elastic.co/t/need-to-test-a-index-with-terabytes-of-data-how-can-i-do/272787/8 "2021-05-24T08:30:53Z")
We want to test sending 2T of specific data to an index to see how large the cluster can reach.Now I have solved this problem, but I had a puzzle during the testing. first question: Does the final result of throughput include replicas? I think the result was only primary shard and it seems according to samples to culculate: sum(bulk\_size)/time\_period. Does this right? I have read [How Write throughput is calculated in Rally - #2 by dliappis](https://discuss.elastic.co/t/how-write-throughput-is-calculated-in-rally/188997/2) second question: When the index\_append start, i use iostat to monitor the io, sometimes the readbyte is zero, why? the bulk\_indexing\_client\_num is 64. ![image](https://us1.discourse-cdn.com/elastic/original/3X/f/a/fa91545b54c26cf600249db0f4facf9153a9dd47.png) third question: How can I know rally has start the amount of clients that I set? --- _[View the full topic](https://discuss.elastic.co/t/need-to-test-a-index-with-terabytes-of-data-how-can-i-do/272787)._