The easiest way to troubleshoot disk IO performance problems is to run an IO test.
There are many tools available for this but we recommend:
You can also find more IO testing tools here: https://www.raymond.cc/blog/measure-actual-hard-disk-perfomance-under-windows/ and here: https://technet.microsoft.com/en-us/library/cc966412.aspx
To live up to server requirements you need high performance hard drives on your VisionFlow servers, especially on the database and SAN server, at least 100 MB/s but preferably faster.
For database IO tests it is better to use another tool than CrystalDiskMark since the database uses really small data chunk sizes. SQL Server does a lot of random stuff in 8KB chunks, and 64KB chunks. Instead there are better tools for IO testing the database. Here is some more information: https://www.brentozar.com/archive/2008/09/finding-your-san-bottlenecks-with-sqlio/
If you need help interpreting the disk IO data you can send them along to our support team.