VM storage placement
The recommendation is to create a big CSV volume. CSV spreads across multiple disk spindles and it will give great storage performance for VMs, as opposed to creating volumes based on the VHD purpose (for example, OS, data, and logs).
If Storage Spaces Direct is used, It's recommended to make the number of volumes a multiple of the number of servers in your cluster. For example, if you have 4 servers, you will experience more consistent performance with 8 total volumes than with 7 or 9.