What must be used when deploying VxRail with a customer-supplied VDS?

An S SeriesVxRail cluster has just been deployed. When attempting to enable compression, the option is grayed out.
What is the cause of this situation?

For which components in a VxRail environment can log files be created using vCenter vSphere Client when the VxRail Manager is unavailable?

What is not a requirement for a VxRail External vCenter deployment?

A systems engineer needs to ensure that the VxRail system is healthy and any issues found are addressed prior to starting an upgrade process. Where in the vSphere Client can they review alarms and overall vSAN health?