A. You can verify your Exchange single-instance storage ratio by viewing the Single-Instance-Ratio counter for the MSExchangeIS-Private and MSExchangeIS-Public objects. A ratio of 1 means you aren't seeing any benefits by using single-instance storage, and every message is already only stored once. A ratio of 2 means that on average, every message stored using single-instance storage exists in two mailboxes, so the technology is saving you some space.