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2. Comparing SRM with
Stretched Clusters
Finding the right solution for your organisation’s needs
Scott Lowe, VCDX 39
vExpert, Author, Blogger, Geek
http://blog.scottlowe.org / Twitter: @scott_lowe

3. Agenda
• Quick review of terminology
• Comparing SRM and vMSC requirements
• Comparing SRM and vMSC advantages
• Comparing SRM and vMSC disadvantages
• Mixing SRM and vMSC

4. RPO versus RTO
• RPO = Recovery Point Objective
• RPO is a measure of how much data loss the organisation is
willing to sustain
• RTO = Recovery Time Objective
• RTO is a measure of how long of a wait the organisation is
willing to tolerate before recovery is complete

5. DR versus DA
• DA = Disaster avoidance
• Seeks to protect apps/data before a disaster occurs
• Howoften do you know before a disaster is going to
occur?
• DR = Disaster recovery
• Seeks to recover apps/data after a disaster occurs
• Think of DA as vMotion and DR as vSphere HA

6. Requirements for vMSC
• Some form of supported synchronous active/active storage
architecture
• Stretched Layer 2 connectivity between sites
• 622 Mbps bandwidth (minimum) between sites
• Lessthan 5 ms latency between sites (10 ms with vSphere 5
Enterprise Plus/Metro vMotion)
•A single vCenter Server instance

7. Requirements for SRM
• Some form of supported storage replication (synchronous or
asynchronous)
• Layer 3 connectivity
• Nominimum inter-site bandwidth requirements (driven by
SLA/RPO/RTO)
• No
maximum latency between sites (driven by SLA/RPO/
RTO)
• At least two vCenter Server instances

8. Advantages of vMSC
• Thepossibility of non-disruptive workload migration (disaster
avoidance)
• No need to deal with issues changing IP addresses
• Potentialfor running active/active data centres and more
easily balancing workloads between them
• Typically a near-zero RPO with RTO of minutes
• Requires only a single vCenter Server instance

9. Advantages of SRM
• Defined startup orders (with prerequisites)
• No need for stretched Layer 2 connectivity (but supported)
• Theability to simulate workload mobility without affecting
production
• Supports
multiple vCenter Server instances (including in
Linked Mode)

10. Disadvantages of vMSC
• Greaterphysical networking complexity due to stretched
Layer 2 connectivity requirement
• Greater
cost resulting from higher-end networking
equipment, more bandwidth, active/active storage solution
• No ability to test workload mobility
• Operational overhead from management of DRS host affinity
groups
• Supports only a single vCenter Server instance

11. Disadvantages of SRM
• Typically higher RPO and RTO than stretched clusters
• Workload mobility is always disruptive
• Requires at least two vCenter Server instances
• Operationaloverhead from managing protection groups and
protection plans

12. What about a mixed
architecture?
• It
can be done, but it has its own set of design
considerations
• For any given workload, it's an “either/or” situation

13. Diagram of a mixed
architecture

14. Additional Resources
• BCO2479 from VMworld 2011 also takes up comparing
SRM and vMSC
• Any of my stretched cluster presentations (all available on my
site, blog.scottlowe.org) discuss pros/cons and design
considerations

15. Questions &
Answers

16. Thank you!