“ThevCenter Server Appliance is a preconfigured linux virtual machine, which is optimized for running vCenter Serverand the associated services on Linux.”
Detailed VMware overview of VCSA found here .
The followingtables outline the latest sizing requirements forVCSA 6.0 (VMware VCSA Sizing KB) , both Embedded and External.
Embedded= vCenter + PSC running on the same Linux based appliance.
External= PSC running on a dedicated Linux based appliance.
Embedded VCSA Sizing:

External VCSA Sizing:


Resizing theVCSAMemory and CPUis supported, although it is advised to size your VCSA for future growth and avoid this scenario if possible. If you start at for example a TINY VCSA configuration and you now have a requirement to jump to a higher spec, then you can increase the CPU&Memory based on the sizing detailed above for S/M/L. For example,if have deployed a SMALL VCSA and you now require a Medium sized VCSA, you can modifythe CPU/Memory to 8/24. This change can be achieved by shutting down and editing the hardware properties of the VCSA itself.
William Lam’s Post covers the Memory and CPU resizing topic in some detailhere: Dynamic memory resizing for vCenter Server 6.0
In the case of resizing the VCSA storage requirements, please see the following VMware KB & Virtnet Blog:
Increasing the disk space for the VMware vCenter Server Appliance in vSphere 6.0
How to Increase VCSA External PSC Disk Space in vSphere 6