Looks like $2B of savings are from reducing the number of servers (200,000 servers earlier to 70,000 now). That has nothing to do with the advantages of a private cloud over public, etc. They were just over-deployed and by reducing the number of servers they would have enjoyed similar savings no matter where they were running them.
In fact they could have saved even more, and earlier, if they had already been in the public cloud, where you can just spin down the VMs and stop paying for them. In your own data center, a server is already sunk cost that you cannot entirely eliminate just by shutting it down.
In fact they could have saved even more, and earlier, if they had already been in the public cloud, where you can just spin down the VMs and stop paying for them. In your own data center, a server is already sunk cost that you cannot entirely eliminate just by shutting it down.