Multi-Site Clustering for Hyper-V Disaster Recovery Greg Shields, MVP, vExpert Senior Partner Concentrated Technology

About the speaker  Administrator – Managed environments ranging from a few dozen to many thousands of users…  Consultant – Hands-on and Strategic…  Speaker – TechMentor, Tech Ed, Windows Connections, MMS, VMworld, ISACA, others…  Analyst/Author – Fourteen books and counting…  Columnist – TechNet Magazine, Redmond Magazine, Windows IT Pro Magazine, TechTarget Online, others…  All-around good guy… Over 15 years of Windows experience

What Makes a Disaster? It causes a server or an entire rack of servers to inadvertently and rapidly power down Which of the following would you consider a disaster? Interrupts the functionality of your datacenter for an extended period of time It’s immediately ceasing all processing on that server Impacts your datacenter and causes damage. That damage causes the entire processing of that datacenter to cease It causes problems with a service, shutting down that service and preventing some action from occurring on the server

What Makes a Disaster? Which of the following would you consider a disaster? It causes a server or an entire rack of servers to inadvertently and rapidly power down It’s immediately ceasing all processing on that server It causes problems with a service, shutting down that service and preventing some action from occurring on the server Just a bad day…

What Makes a Disaster?  Your decision to “declare a disaster” and move to “disaster ops” is a major one  The technologies used for disaster protection are different than those used for high-availability More complex More expensive  Failover and failback processes involve more thought You might not be able to just “fail back” with a click of a button

Microsoft has not done a good job of explaining this fact! Some Hyper-V hosts Some networking and storage Virtual machines that Live Migrate around Multi-Site Hyper-V == Single-Site Hyper-V Multi-site Hyper-V looks very much the same as single-site Hyper-V But there are some major differences too… VMs can Live Migrate across sites Sites typically have different subnet arrangements Data in the primary site must be replaced with the DR site Clients need to know where your servers go!

Constructing Site-Proof Hyper-V: Three Things  Once you have these three things, layering Hyper-V atop is easy. Storage mechanism Replication mechanism Target Servers & Cluster At a very high level, Hyper-V disaster recovery is three things

Constructing Site-Proof Hyper-V: Three Things Storage Device(s) Replication Mechanism Target Servers

Thing 1: A Storage Mechanism Typically, two SANs in two different locations Backup SAN doesn’t necessarily need to be of the same size or speed as the primary SAN Fibre Channel, iSCSI, FCoE, heck JBOD Similar model or manufacturer Similarity  proper replication Replicated ≠ Full data (not always) DR – not for everything! DR E nvironments: Where Old SANs Go To Die!

Thing 2: A Replication Mechanism Replication between SANs must occur 1. Synchronously 2. Asynchronously Changes are made on one node at a time Subsequent changes on primary SAN must wait for ACK from backup SAN Changes on backup SAN will eventually be written Changes queued at primary SAN to be transferred at intervals

Thing 2: A Replication Mechanism ●Changes are made on one node at a time. Subsequent changes on primary SAN must wait for ACK from backup SAN. 1. Synchronously

Thing 2: A Replication Mechanism ●Changes on backup SAN will eventually be written. Are queued at primary SAN to be transferred at intervals. 2. Asynchronously

Food for Thought Synchronous ●Assures no loss of data ●Requires a high-bandwidth and low-latency connection ●Write and acknowledgement latencies impact performance ●Requires shorter distances between storage devices ●Potential for loss of data during a failure ●Leverages smaller-bandwidth connections, more tolerant of latency ●No performance impact ●Potential to stretch across longer distances Your Recovery Point Objective makes this decision… Which would you choose? Why? Asynchronous

Thing 2½: Replication Processing Location 1. Storage Layer ●Replication processing is handled by the SAN itself ●Agents are often installed to virtual hosts or machines to ensure crash consistency ●Easier to set up, fewer moving parts. More scalable ●Concerns about crash consistency 2. OS / Application Layer ●Replication processing is handled by software in the VM OS ●This software also operates as the agent ●More challenging to set up, more moving parts. More installations to manage/monitor. Scalability and cost are linear ●Fewer concerns about crash consistency There are also two locations for replication processing…

Thing 3: Target Servers and a Cluster  Finally are target servers and a cluster in the backup site.

Clustering’s Sordid History Windows NT Microsoft Cluster Service “Wolfpack” - “As the corporate expert in Windows clustering, I recommend you don’t use Windows clustering” - Microsoft Cluster Service “Wolfpack” - “As the corporate expert in Windows clustering, I recommend you don’t use Windows clustering” Windows 2000 Greater availability, scalability. Still painful Windows Added iSCSI storage to traditional Fibre Channel - SCSI Resets still used as method of last resort (painful) - Added iSCSI storage to traditional Fibre Channel - SCSI Resets still used as method of last resort (painful) Windows Eliminated use of SCSI Resets - Eliminated full-solution HCL requirement - Added Cluster Validation Wizard and pre-cluster tests - Clusters can now span subnets (ta-da!) - Eliminated use of SCSI Resets - Eliminated full-solution HCL requirement - Added Cluster Validation Wizard and pre-cluster tests - Clusters can now span subnets (ta-da!) Windows 2008 R2 - Improvements to Cluster Validation Wizard and Migration Wizard - Additional cluster services - Cluster Shared Volumes (!) and Live Migration (!) - Improvements to Cluster Validation Wizard and Migration Wizard - Additional cluster services - Cluster Shared Volumes (!) and Live Migration (!)

So, What IS a Cluster?

Quorum Drive & Storage for Hyper-V VMs

So, What IS a Multi-Site Cluster?

Quorum: Clustering’s Most Confusing Configuration  Ever been to a Kiwanis meeting…?  A cluster “exists” because it has quorum between its members. Quorum is achieved via a voting process  If a cluster “loses quorum”, the entire cluster shuts down and ceases to exist. This happens until quorum is regained  Multiple quorum models exist Different clubs – different rules Different clusters – different rules Different than resource failover

Four Options for Quorum 1.Node and Disk Majority 2.Node Majority 3.Node and File Share Majority 4.No Majority: Disk Only

Quorum in Multi-Site Clusters  Node and Disk Majority  Node Majority  Node and File Share Majority  No Majority: Disk Only Microsoft recommends using the Node and File Share Majority model for multi-site clusters  This model provides the best protection for a full-site outage  Full-site outage requires a file share witness in a third geographic location

Quorum in Multi-Site Clusters  Use the Node and File Share Quorum ●Prevents entire-site outage from impacting quorum. ●Enables creation of multiple clusters if necessary. Third Site for Witness Server

I Need a Third Site? Seriously?  What happens if you put the quorum’s file share in the primary site? ●The secondary site might not automatically come online after a primary site failure ●Votes in secondary site < Votes in primary site Here’s where Microsoft’s ridiculous quorum notion gets unnecessarily complicated…

I Need a Third Site? Seriously?  What happens if you put the quorum’s file share in the secondary site? ●A failure in the secondary site could cause the primary site to go down. ●Votes in secondary site > votes in primary site. This problem gets even weirder as time passes and the number of servers changes in each site Here’s where Microsoft’s ridiculous quorum notion gets unnecessarily complicated…

I Need a Third Site? Seriously? Third Site for Witness Server

Multi-Site Cluster Tips/Tricks ●Make sure your servers fail over to servers in the same site first ●But also make sure they have options on failing over elsewhere Manage Preferred Owners & Persistent Mode options

Multi-Site Cluster Tips/Tricks ●Failback is a great solution for resetting after a failure ●But Failback can be a massive problem-causer as well ●Its effects are particularly pronounced in Multi-Site Clusters ●Recommendation: Turn it off, (until you’re ready) Consider carefully the effects of Failback

More Multi-Site Cluster Tips/Tricks Resist creating clusters that support other services Use disk “dependencies” as Affinity/Anti-Affinity rules Add Servers in Pairs ● A Hyper-V cluster is a Hyper-V cluster is a Hyper-V cluster ●Hyper-V all by itself doesn’t have an elegant way to affinitize ●Setting disk dependencies against each other is a work-around ●Ensures that a server loss won’t cause site split brain ●This is less a problem with the File Share Witness configuration

Multi-Site Cluster Tips/Tricks  Segregate traffic!!!

Most Important! ●Crossing subnets also means: changing IP address, subnet mask, gateway, etc., at new site ●Automatically done by using DHCP and dynamic DNS OR must be manually updated ●DNS replication is also a problem. Clients will require time to update their local cache ●Consider reducing DNS TTL or clearing client cache Ensure that networking remains available when VMs migrate from primary to backup site  Clustering can span subnets! - This is good, but only if you plan for it…

Multi-Site Clustering for Hyper-V Disaster Recovery Greg Shields, MVP, vExpert Senior Partner Concentrated Technology

Enjoy and share this material  Feel free to promote this material  Recommend your peers to pass certification  Blog, Tweet and share this material and your experience on Facebook  You’re an Expert? We will be happy to have you as Backup Academy contributor. Apply here.here Web: Twitter: BckpAcademyBckpAcademy Facebook: backup.academybackup.academy