I think that the best test is to: 0. Set only 1 change in the infrastructure 1. Automatically create your VM 2. Install the necessary application on the VM from point 1 3. Restore from backup the state of the App 4. Run a typical workload on the app - for example a bunch of queries that are pushed against a typical DB 5. Measure performance during point 4 (for example time of execution) 6. Start over Anything else is a waste of time. Best Regards, Strahil Nikolov На 24 юли 2020 г. 13:26:18 GMT+03:00, Stefan Hajnoczi <stefanha@redhat.com> написа:
On Thu, Jul 23, 2020 at 07:25:14AM -0700, Philip Brown wrote:
Usually in that kind of situation, if you dont turn on sync-to-disk on every write, you get benchmarks that are artificially HIGH. Forcing O_DIRECT slows throughput down. Dont you think the results are bad enough already? :-}
The results that were posted do not show iSCSI performance in isolation so it's hard to diagnose the problem.
The page cache is used when the O_DIRECT flag is absent. I/O is not sent to the disk at all when it can be fulfilled from the page cache in memory. Therefore the benchmark is not an accurate indicator of disk I/O performance.
In addition to this, page cache behavior depends on various factors such as available free memory, operating system implementation and version, etc. This makes it hard to compare results across VMs, different machines, etc.
Stefan