the Exadata eighth rack is actually hardware identical to a quarter rack . It is just that half of the cpus, half of the disks and half of the flash have been disabled in software/firmware. By buying an eighth rack you commit to using only a certain portion of the hardware. An attempt to upgrade in the manner you are describing would be a violation of your contract. If you wish to upgrade to a quarter it is basically just a call to oracle and they "flip the switch" to enable the remaining hardware. As far as I know currently this is an all or nothing proposition. I.e you get all the cpu ,disk and flash in one package at one price. If you need the additional compute but not the additional disk or flash I am not sure if you can cut a deal with Oracle for the same. However its not in the published game plan.
Yes you can upgrade from an eighth to a quarter. This is designed as a field upgrade as the hardware is already in your machine but only needs to be enabled.
To quote from the doc in the link:
"Additional Hardware Components Present In The Eighth Rack Are Enabled With The Upgrade"
Thanks for the reply. I'm not going to add cpus on my own. I'm sure I have to purchase database licenses accordingly and need cofiguration team
to turn the switch on. Just wanted to know if I have to purchase another database servers for quarter and keep existing eighth servers remained
which means four servers in place, actually two servers with 16-cores and two servers with 8-cores.
Now it made me feel comfortable that a purchase of eighth will be scalable.