The idea to reimage ODA is to refresh the environment without the need to jump from one by one to reach the last available version, or even rescue the system from S.O. failure/crash. The process to do a reimage can be check in the official documentation but unfortunately can be very tricky because the information (the order and steps) are not 100% clear. The idea is to show you how to reimage using version 18 (18.3 in this example), that represents the last available.
Here I cover in raw, undocumented and uncommented mode the process to update and upgrade your Exadata using the last version of everything. AND since Oracle 18c was released to use with Oracle Exadata (from SQL Maria), this post include the Oracle 18c upgrade for Grid Infrastructure and Oracle database binaries installation.
Since one friend was decommissioning one old Exadata X2 (running after the end of life), I used to do some tests and here you will find the commands, outputs, images that I use to (in order):
Apply the patch 188.8.131.52.180116 for Oracle Grid Infrastructure 12.1.
Update the Infiniband switches to last version 2.2.7-1.
Apply the patch for Exadata Storage Server using the last version, 184.108.40.206.0.180125.3.
Apply the patch for Exadata Database Servers using the last version, 220.127.116.11.0.180125.3
Upgrade the Oracle Grid Infrastructure 12.1 to Grid Infrastructure 12.2, applying PSU 18.104.22.168.180116 at same time.
Upgrade the Oracle Grid Infrastructure 12.2 to Oracle Grid Infrastructure 18c.
Install Oracle database binaries for Oracle Database 18c and Create a test Oracle Rac Instance.