Decreasing Exadata core count , X6-2 1/8

Decreasing the core count of Exadata compute nodes can be your issue one day, as Exadata does not let you to do so easily.
Decreasing the core count is not an operation that is frequently done, but still it may necessary some day.
That is, normally when you purchase Exadata and when you decide to have a minimal capacity on demand configuration, these cpu count decreases are done in the deployment phase, but I have seen some customer environment, on which we need to decrease the cpu counts to be aligned with the license terms , even after the deployment.

So the utility we use dbmcli, but we use it with an undocumented force parameter.
Note that, we execute the dbmcli and the commands in both of nodes and reboot the nodes afterwards.
Without using the force argument, dbmcli our the resoucecountrol do not let us to decrease the cpu cores to the minimum ( 8 cores)
Note, we also disable iaasMode just in case;

Here;

[root@ermanexa01~]# dbmcli
DBMCLI: Release  - Production on Mon Aug 15 15:56:16 EEST 2016
Copyright (c) 2007, 2014, Oracle.  All rights reserved.
DBMCLI> ALTER DBSERVER pendingCoreCount = 8 force
DBM-10022: At least 26 physical cores need to be active in order to support IaaS.
DBMCLI> ALTER DBSERVER iaasMode = "off"
DBServer exadb01 successfully altered
DBMCLI> ALTER DBSERVER pendingCoreCount = 8 force
DBServer exadb01 successfully altered. Please reboot the system to make the new pendingCoreCount effective.