High page fault, slow query/ insert during background index creation in MongoDB
Index builds can impact the performance of your database. While background index builds will not block read or writes, it is not correct to say that "index creation should not affect [the performance of] read/write".

Building an index will require paging the entire collection through memory; this is cause of the page faults being seen. You will likely want to only build a single index at a time to reduce the impact of this process.