I would like to convert all the switches in my functioning network from PVST to RSTP.
Are PVST and RSTP compatible?
I understand PVST will create Spanning tree for each VLAN, RSTP will create one big spanning tree for all VLANs but I m not sure how they work in the background.
Is there any other trouble I need to be aware of ?
PVST and RSTP are compatible, but it can be a bit tricky to have both function at the same time. RSTP is mapped to PVST VLAN1 so you must make sure that VLAN1 is enabled on any trunks between RSTP and PVST regions. Also if you have any PVST regions separated by an RSTP region, the PVST BPDUs are transparently forwarded across the RSTP region. Any interoperation between these two protocols should only be done as a temporary measure during migration from one to the other. Ultimately you should use either one or the other.
Cisco provides some recommendations concerning the migration from one protocol to another in the following documentation: