Explanation
References: https://cloud.oracle.com/networking/vcn/faq

Explanation
A fault domain is a grouping of hardware and infrastructure within an availability domain. Each availability domain contains three fault domains. Fault domains provide anti-affinity: they let you distribute your instances so that the instances are not on the same physical hardware within a single availability domain. A hardware failure or Compute hardware maintenance event that affects one fault domain does not affect instances in other fault domains. In addition, the physical hardware in a fault domain has independent and redundant power supplies, which prevents a failure in the power supply hardware within one fault domain from affecting other fault domains.
To control the placement of your compute instances, bare metal DB system instances, or virtual machine DB system instances, you can optionally specify the fault domain for a new instance or instance pool at launch time. If you don't specify the fault domain, the system selects one for you. Oracle Cloud Infrastructure makes a best-effort anti-affinity placement across different fault domains, while optimizing for available capacity in the availability domain. To change the fault domain for an instance, terminate it and launch a new instance in the preferred fault domain.
Use fault domains to do the following things:
Protect against unexpected hardware failures or power supply failures.
Protect against planned outages because of Compute hardware maintenance.

Explanation
You can use the Console or API to import exported images from Object Storage. To import an image, you need read access to the Object Storage object containing the image.
during the Import you can select the Launch mode:
For custom images where the image format is .oci, Oracle Cloud Infrastructure selects the applicable launch mode based on the launch mode for the source image.
For custom images exported from Oracle Cloud Infrastructure where the image type is QCOW2, select Native Mode.
To import other custom images select Paravirtualized Mode or Emulated Mode. For more information, see Bring Your Own Image (BYOI).

Explanation
Oracle Cloud Infrastructure automatically backs up your Autonomous Databases and retains these backups for
60 days. Automatic backups are weekly full backups and daily incremental backups. You can also create manual backups to supplement your automatic backups. Manual backups are stored in an Object Storage bucket that you create, and are retained for 60 days The retention period for manual backups is the same as automatic backups which is 60 days. So we cannot preserve the backup for 12 months
https://docs.oracle.com/en/cloud/paas/autonomous-data-warehouse-cloud/user/backup-manual.html#GUID-D95E

to Increase disk performance by using NVMe disks you can use Dense IO Shape also as the number of CPUs will not change so we should VM.DenseIO2.16