The correct architecture combines S3 versioning, cross-grid replication (CGR), and ILM retention. StorageGRID cross-grid replication operates between two StorageGRID systems connected through grid federation and requires the participating source and destination buckets to have versioning enabled. Critically, CGR creates versioned objects at the destination and replicates the source version ID, preserving the ordering of object versions between the grids. This directly satisfies the requirement to protect all possible versions.

After replication, each grid independently applies its active ILM policy to the objects stored locally. The backup grid can therefore use ILM rules to retain replicated objects for at least 90 days. StorageGRID ILM also supports rules specifically targeting noncurrent versions of versioned S3 objects by using Noncurrent time as the reference time, allowing previous versions to be retained for the required period.

Options A and B are unsuitable because nonversioned buckets cannot preserve every object version. Option C correctly identifies versioning and CGR, but a bucket policy governs access permissions; version retention is instead controlled through ILM or an S3 lifecycle configuration.

Reference topics: Grid Federation → Cross-Grid Replication → S3 Versioning → ILM Rules → Noncurrent Object Versions → Retention Periods