A company needs to protect against data corruption using split mirror snapshots. Their RTO is 15 minutes and RPO is one hour. It takes 15 minutes to…

This scenario requires balancing the Recovery Point Objective (RPO), Recovery Time Objective (RTO), and the time required to create a snapshot. The RPO of one hour dictates the maximum acceptable data loss, meaning a successful snapshot must be completed at least every hour. The RTO of 15 minutes requires that a consistent snapshot is always available to begin the recovery process immediately upon failure.

Since it takes 15 minutes to establish the snapshot, using a single snapshot volume would create a 15-minute window where no consistent, ready-to-use snapshot exists. Using two volumes in an alternating schedule solves this. While one volume is being updated, the other remains online and consistent, ensuring a recovery point is always available to meet the RTO. Scheduling the creation every 60 minutes aligns perfectly with the one-hour RPO, making it the most efficient solution without incurring the unnecessary overhead of more frequent snapshots.

A. Use one snapshot volume and incrementally establish it every 60 minutes.

A failure during the 15-minute snapshot creation would make the previous snapshot 75 minutes old, violating the one-hour RPO.

B. Use one snapshot volume and incrementally establish it every 30 minutes.

For 15 minutes of every 30-minute cycle, the single snapshot volume is being updated and is unavailable for an immediate restore, failing to guarantee the RTO.

D. Use two snapshot volumes and incrementally establish one volume every 30 minutes.

This meets the RPO and RTO but is inefficient. It creates snapshots twice as frequently as required by the one-hour RPO, consuming unnecessary system and network resources.

1. Somasundaram, G., & Shrivastava, A. (Eds.). (2012). Information Storage and Management: Storing, Managing, and Protecting Digital Information in Classic, Virtualized, and Cloud Environments (2nd ed.). Wiley.

Chapter 11, Section 11.2.1, "BC Terminology": Defines RPO as "the point in time to which the systems and data must be recovered... RPO is generally defined in terms of hours." This supports matching the snapshot frequency to the one-hour RPO for efficiency.

Chapter 9, Section 9.3.2, "Uses of Local Replicas": Explains that replicas are used for recovery from data corruption. It emphasizes the need for a consistent, point-in-time copy. The logic of using multiple replicas to ensure one is always consistent and available while another is synchronizing is a direct application of this principle, especially when the synchronization time (15 minutes) is significant.

2. Gibson, G. A. (1996). CS-96-162 Course Syllabus: 15-740 Computer Architecture. Carnegie Mellon University, School of Computer Science.

In course materials discussing storage systems and reliability, the fundamental concept is that a recovery mechanism must have a consistent, available data copy to restore from. The time to create this copy (the 15-minute snapshot establishment) represents a window of vulnerability if only one copy exists, directly impacting the ability to meet a strict RTO. The use of alternating buffers (i.e., two snapshot volumes) is a standard technique to mitigate this.