In both the METADATA and STORAGE phases of hms-mirror the RIGHT cluster will reach down into the LEFT clusters storage layer to either use or copy the data.
hms-mirror access each cluster via JDBC and use the RIGHT cluster for storage layer access.
When the RIGHT cluster is using 'non-impersonation' (hive doas=false), the hive service account on the RIGHT cluster (usually hive) needs access to the storage layer on the LEFT cluster to use this data to support sidecar testing, where we use the data of the LEFT cluster but mirror the metadata.