Currently we are working on Entire SAP landscape using single SAN storage where database of DEV,QAS and production will be stored. Whether the SAN should be used for all databases or it should be for production database only?
Markus Doehr replied
This is something only the hardware vendor can tell you. "Usually" you do a sizing using Quicksizer (http://service.sap.com/quicksizer) and your chosen hardware vendor will suggest the best matching hardware for you (machines + SAN).
You can put all instances on one SAN technically, keep in mind that the performance of the production may be impacted if someone is doing things on the other two systems. However, there are SAN systems, that can do I/O class priorization, we don´t know if you SAN can do that. Check with your vendor.