Unbuffered IO option for ReFS repository

[jzilak]

Hello,

it is possible add support for unbuffered IO for ReFS repository servers? We have repository server with 768GB RAM, and buffered IO causing extremely large dirty pages pool from 5-400GB RAM. We made some tests with robocopy.exe and buffered IO was much slower on ReFS than unbuffered IO. In our tests (we simply copy 15 TB backup repository between two storage groups) performance benefit to unbuffered IO was more than 100MB/s (180MB/s vs. 280MB/s). This throughput can be achieved with public ReFS path KB4016173 and RefsEnableLargeWorkingSetTrim. Private ReFS patch looks like has performance regression with ReFSDisableCachedPins key, but greatly help with delete operations on ReFS during job maintenance phase.

josef