Disaster Recovery – Do you really need one?

 Last week, Microsoft announced the Preview of Capacity Reservation for VMs. You can reserve VM capacity in your DR region to ensure that you have VM resources available to create or turn on your protected VMs using ASR. ASR does not guarantee that your VMs can be turned on in your DR region in the event of disaster recovery. So, capacity reservation is a welcome feature and much needed. However, this is increasing the cost of your solution again.

  • Cost factors
    • VM cost
    • ASR protected VM cost
    • Capacity Reservation Cost ( as same as your actual VM cost)
    • other costs

Note: DR is not just the VMs but including other components. I did not provide the details above because it applies to both the options.

Hmm.. Can we plan a DR cost-effectively in Azure? Let’s take a look:

  • Option 1 : with ASR
    1. Deploy your production VMs in the primary region
    2. Get Azure Reserved Instances in the DR region along with your primary region.
    3. ASR-protected VMs. 
    4. Get a capacity reservation for your DR VMs.

This option provides you guaranteed VM resources to turn on your ASR-protected VMs during the region disaster recovery. However, it is adding additional cost of ASR-protected VM cost and capacity reservation. We are using RIs to save the VM and its capacity reservation costs.

  • Option 2 : Active – Active
    1. Run the active-active DR from both Primary and Secondary. It does not matter where you are running your non-production in this case. 
    2. Get Azure Reserved Instances
    3. No Capacity reservation.

You are saving the cost of ASR-protected VMs, and Capacity Reservation costs here with option two and, of course, reducing the RTO and RPO to nearly Zero. However, there may be some extra charges, including data transfer. 

Would you go for Option 1 and Option 2?

It doesn’t matter which one you select; Good effective DR is becoming more expensive day by day. We should ask ourselves if we need DR when we have availability zones spread across a Public Cloud region? We should focus more on planning high availability utilizing the multi-zone features than planning for an expensive DR unless it is mission-critical. I suggest you read my other blog on this topic.

I do not encourage planning an ASR-based DR without capacity reservation. But it adds additional cost, and that becomes a more expensive affair. How about active-active region DR? It is expensive as well. I suggest you review your DR cases carefully to check your revenue loss in the event of DR versus investment required for anticipating a DR that may not be happening. 

Please send me your comments, and let’s brainstorm the ideas together.


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