Your customer needs to ensure that their data is available on the Exadata machine during...

Your customer needs to ensure that their data is available on the Exadata machine during updates. The customer wants to be able to update one server at a time but still be protected against single-node server failure. This means that they need a redundancy level that can tolerate at least one disk failure without losing data availability or performance. Therefore, the best option for them is normal redundancy . Normal redundancy provides two-way mirroring by default, which means that each data extent has a primary copy and a mirror copy on different disks in different failure groups1. A failure group is a subset of disks within a disk group that are likely to fail at the same time due to common dependencies2. On Exadata Database Machine , each Storage Server is considered as a failure group by default2. This means that if one Storage Server fails or needs to be updated , the data on its disks can still be accessed from another Storage Server that has the mirror copies of the same data extents2. Therefore, normal redundancy ensures data availability and performance during updates or single-node server failures.

https://docs.oracle.com/en/engineered-systems/exadata-database-machine/sagug/exadata-administering-asm.html