exploring stretched clusters
TRANSCRIPT
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Before we start
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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
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Part 1: Stretched Cluster Or SRM?
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• 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
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• 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
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• 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
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• 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
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• 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
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• 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
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• 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
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• 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
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• 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
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• 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
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• 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?
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Diagram of a mixed architecture
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Part 2: Building Stretched Clusters
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• vSphere recommendations
• Storage recommendations
• Networking recommendations
• Operational recommendations
Part 2 Agenda
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• Use vSphere 5
• Use DRS host affinity groups
• Run vSphere HA with N+2 capacity
vSphere recommendations
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• vSphere 5 eliminates some vSphere HA limitations
• vSphere 5 introduces the vMSC HCL category
Use vSphere 5
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• 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
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• 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
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• 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
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• 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
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• 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
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• 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
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• 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
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• Account for backup/restore in your design
• Handle inter-site vMotion carefully
• Don't split multi-tier apps across sites
Operational recommendations
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• 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
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• 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
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Questions & Answers
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