Exploring Stretched Clusters

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Before we start


EXPLORING STRETCHED CLUSTERS

Scott Lowe, VCDX 39CTO, VMware Affinity TeamAuthor, Mastering VMware vSphere 5Blogger, http://blog.scottlowe.org

Examining the use of stretched clusters in a VMware vSphere environment

http://blog.scottlowe.org

http://blog.scottlowe.org


Part 1: Stretched Cluster Or SRM?


• Quick review of terminology

• Comparing SRM and vMSC requirements

• Comparing SRM and vMSC advantages

• Comparing SRM and vMSC disadvantages

• Mixing SRM and vMSC

Part 1 Agenda


• vMSC = vSphere Metro Stretched Cluster

• Introduces some new terms:• Uniform access = "stretched SAN"

• Non-uniform access = "distributed virtual storage"

• Provides boundaries for supportability of stretched cluster configurations

New vMSC HCL category


• RPO = Recovery Point Objective

• RPO is a measure of how much data loss the organization is willing to sustain

• RTO = Recovery Time Objective

• RTO is a measure of how long of a wait the organization is willing to tolerate before recovery is complete

RPO versus RTO


• DA = Disaster avoidance• Seeks to protect applications and data before a

disaster occurs

• How often do you know before a disaster is going to occur?

• DR = Disaster recovery• Seeks to recover applications and data after a

disaster occurs

• Think of DA as vMotion and DR as vSphere HA

DR versus DA


• Some form of supported storage replication (synchronous or asynchronous)

• Layer 3 connectivity

• No minimum 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

Requirements for SRM


• Some form of supported synchronous active/active storage architecture

• Stretched Layer 2 connectivity

• 622Mbps bandwidth (minimum) between sites

• Less than 5 ms latency between sites (10 ms with vSphere 5 Enterprise Plus/Metro vMotion)

• A single vCenter Server instance

Requirements for vMSC


• Defined startup orders (with prerequisites)

• No need for stretched Layer 2 connectivity (but supported)

• The ability to simulate workload mobility without affecting production

• Supports multiple vCenter Server instances (including in Linked Mode)

Advantages of SRM


• The possibility of non-disruptive workload migration (disaster avoidance)

• No need to deal with issues changing IP addresses

• Potential for running active/active data centers and more easily balancing workloads between them

• Typically a near-zero RPO with RTO of minutes

• Requires only a single vCenter Server instance

Advantages of vMSC


• Typically higher RPO and RTO than stretched clusters

• Workload mobility is always disruptive

• Requires at least two vCenter Server instances

• Operational overhead from managing protection groups and protection plans

Disadvantages of SRM


• Greater physical 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

Disadvantages of vMSC


• It can be done, but it has its own set of design considerations

• For any given workload, it's an “either/or” situation

What about a mixed architecture?


Diagram of a mixed architecture


Part 2: Building Stretched Clusters


• vSphere recommendations

• Storage recommendations

• Networking recommendations

• Operational recommendations

Part 2 Agenda


• Use vSphere 5

• Use DRS host affinity groups

• Run vSphere HA with N+2 capacity

vSphere recommendations


• vSphere 5 eliminates some vSphere HA limitations

• vSphere 5 introduces the vMSC HCL category

Use vSphere 5


• Allows you to mimic site awareness

• Use PowerCLI to address manageability concerns

• Use "should" rules instead of "must" rules

Use vSphere DRS host affinity groups


• Use some sort of unique property to "group" VMs

• Use this "grouping" to automate VM placement into groups

• Run the PowerCLI script regularly to ensure correct VM group assignment

Using PowerCLI with host affinity groups


• Use storage from vMSC category

• Be aware of storage performance considerations

• Account for storage availability

• Plan Storage DRS carefully

• Use profile-driven storage

Storage recommendations


• Consider cross-connect topology

• Ensure multiple storage controllers at each site for availability

• Provide redundant and independent inter-site storage connections

• With VPLEX, use the third-site cluster witness

Account for storage availability


• Align datastore clusters to site/array boundaries

• Don't combine stretched/non-stretched datastores

• Understand the impact of SDRS on your storage solution

Plan Storage DRS carefully


• Use user-defined capabilities to model site topology

• Create VM storage profiles to provide site affinity

• Can help avoid operational concerns with VM placement

Use profile-driven storage


• Plan for different traffic patterns

• Where possible, separate management traffic onto a vSwitch

• Incorporate redundant and independent inter-site network connections

• Minimize latency as much as possible

Networking recommendations


• Account for backup/restore in your design

• Handle inter-site vMotion carefully

• Don't split multi-tier apps across sites

Operational recommendations


• Consider a solution with client-side deduplication to reduce WAN traffic

• A mechanism to reduce restore traffic would be nice to have as well

• Might be able to leverage storage solution itself for restores• Restore to local side

• Allow storage solution to replicate to remote side

Backup/restore for stretched clusters


• An inter-site vMotion will impact DRS host affinity rules

• An inter-site vMotion could require storage configuration updates

• Review inter-site vMotions to:• Reconcile DRS host affinity rules and VM locations

• Reconcile storage availability rules and VM locations

• Impact on other operational areas

Handling inter-site vMotion


Questions & Answers


Technology

Exploring Stretched Clusters