I'm testing performance of a clustered NFS server using a 4.15 client. My test setup involves running IOZone to write a 30GB file to the server over NFSv3. The issue is that we occasionally see bad performance, especially when unstable writes are enabled on the server. Based on observing the network traffic, we've seen the write I/O size during good runs stay around 1MB (which is how we've mounted) but in the bad runs we see often see dips in write size (down to even 4KB or 8KB) towards the end of the test. I'm trying to understand why we see the dip in I/O size from the NFS client as it seems to be related to the decrease in performance. Any ideas what could cause it? Also, any suggestions on where I should look to start learning about the way the Linux NFS client and page cache handle unstable writes internally? Thanks, Ted Carpenter
