To Stretch or Not to Stretch?

Discusses the pros and cons of stretched VMware vSphere clusters

Transcript

1. Before we start • Get involved! • If you use Twitter, feel free to tweet about this session (use hashtag #VMUG) • I encourage you to take photos or videos of today’s session and share them online • This presentation will be made available online after the event
2. To Stretch or Not to Stretch? Examining the pros and cons of stretched VMware vSphere clusters Scott Lowe, VCDX 39 vExpert, Author, Blogger, Geek http://blog.scottlowe.org / Twitter: @scott_lowe
3. Agenda • A quick review of stretched clusters • Stretched cluster considerations • Looking forward • Questions and answers
4. Stretched Cluster Review A quick review of stretched clusters
5. Stretched Cluster Review • A stretched cluster is a cluster with ESX/ESXi hosts in different physical locations, usually different geographic sites • Stretched clusters are typically built as a way to create “active/active” data centers in order to: • Provide high availability across sites • Do dynamic workload balancing across sites
6. Stretched Cluster Review • HA/DRS are not required in a stretched cluster, although they are typically deployed • Most pros and cons of stretched clusters stem directly from the use of HA/DRS • Stretched clusters are not a requirement for long-distance vMotion
7. Stretched Cluster Considerations Evaluating the use of stretched clusters
8. Stretched Cluster Considerations: Storage • Active/active data centers require read/write storage at both ends • Storage performance suffers otherwise • Storage vMotion required to fix the performance hit • Only a few products capable of providing read/write storage at both ends of the stretched cluster • Solutions are generally limited to synchronous (~100km) distances
9. Stretched Cluster Considerations: Storage
10. Stretched Cluster Considerations: Storage VM Active Storage
11. Stretched Cluster Considerations: Storage VM Active Storage
12. Stretched Cluster Considerations: Storage VM Active Storage
13. Stretched Cluster Considerations: HA • VMware HA can provide cross-site failover • However, VMware HA is not currently “site aware” • You can’t control failover destination • Can’t designate or define things like: • Per-site failover capacity • Per-site failover hosts • Per-site admission controls
14. Stretched Cluster Considerations: HA • No more than 8 hosts in HA-enabled stretched clusters or you’ll run afoul of HA primary node limitations • Can only deploy 4 hosts or less per site per cluster • Ensures distribution of HA primary nodes • No supported method to increase the number of primary nodes or to specify HA primary nodes
15. Stretched Cluster Considerations: DRS • You can balance load across sites using DRS • However, VMware DRS (like HA) is not “site aware” • DRS host affinity rules can mimic “site awareness” • DRS host affinity rules are not dynamic • DRS host affinity rules create administrative overhead
16. Stretched Cluster Considerations: Networking • Stretched clusters add a lot of networking complexity • More complex network configuration is required to provide Layer 2 adjacency (or its equivalent) • More complex networking required to address routing issues created by VM mobility • Technologies to address these concerns are new (OTV, LISP) and require networking expertise to configure and maintain
17. Router Router L2 Tunnel Stretched Cluster Considerations: Networking VM
18. Router Router L2 Tunnel Stretched Cluster Considerations: Networking VM
19. Router Router L2 Tunnel Stretched Cluster Considerations: Networking VM
20. Router Router L2 Tunnel Stretched Cluster Considerations: Networking VM
21. Stretched Cluster Considerations: Operations • Movement of VMs between sites (perhaps due to HA/DRS) could impact other areas: • Backups • Personnel/support • Disaster recovery/replication
22. Looking Forward… What will the future bring? Some speculation on the future of stretched clusters
23. The Future of Stretched Clusters • HA/DRS are simultaneously “greatest strength and greatest weakness” for stretched clusters • Stretched clusters will directly benefit from any improvements to HA/DRS in these areas: • Primary/secondary node behaviors • HA admission control algorithm • More scalable/dynamic DRS host affinity rule management (policy-based placement)
24. The Future of Stretched Clusters • Stretched clusters will benefit from further networking developments such as: • LISP (or equivalent) to decouple network routing from network identity • OTV, VPLS, or other equivalents to enable Layer 2 adjacency • In the longer-term future, the need for Layer 2 adjacency needs to be addressed and resolved
25. The Future of Stretched Clusters • Improvements in storage functionality will help stretched clusters • Active/active read-write storage at greater distances • Better handling of “split brain” scenarios • Better/more direct integration with replication for topologies with >2 sites (Sync-Sync-Async, for example)
26. Questions & Answers
27. Thank You