TPT Instances - How this works? - response (4) by feinholz

We do support the use of multiple instances reading from a single file. We have seen some nice performance improvement (due to the operating system caching the I/O reads). However, YMMV.
As far as multiple instances reading from different files, yes you can get good performance improvements by using more instances. However, you have other issues to deal with. Namely, disk head contention. If all files are on the same drive, the disk head contention and other operating system environmental issues might affect performance.
So, guarantee? No, but in a lot of cases, yes.
When using multiple instances to read a single file, yes the rows are distributed evenly across the reader instances.
When using multiple instances to read from multiple files, we load balance the files across the instances according to the file sizes.