VMworld 2012: Avoiding 19 Biggest HA & DRS Mistakes INF-VSP1232

Greg Shields, Concentrated Technology partner. This session focused on the main HA/DRS mistakes that people make when virtualizing their infrastructure. Greg is a great speaker and also has presented sessions at TechEd and other conferences. HA/DRS settings are so easy to set and forget, or forget to set, that everyone should review all 19 mistakes and make sure you aren't doing them in your environment.

• HA/DRS solves two problems: Protection from unplanned downtime; Load Balancing and defragmentation of resources.
• Large number of environments have configured HA/DRS settings incorrectly.
• Mistake #1: Not planning for HW evolution.
• vMotion requires similar processors.
• Always set EVC mode
• Mistake #2: Not planning for svMotion
• VMs cannot have snapshots
• VM disks must be persistent mode or RDMs
• Host must have sufficient resources to support two instances of the VMs running concurrently.
• Must be licensed and correctly configured with vMotion
• Host must have access to both source and target datastores
• Mistake #3: Not Enough Cluster Hosts
• For HA failover requires additional "wasted" hardware resources
• Must plan for cluster reserve
• A fully prepared cluster must set aside one full server's worth of resources in preparation for HA.
• Enable admission control - Super important to enable. Will disallow starting VMs when resources are exhausted.
• Set host failures cluster tolerates to 1 (or more). Ensures you always have at least one hosts's worth of resources available.
• Mistake #4: Setting Host Failures the Cluster Tolerates to 1
• Not all your VMs are priority one
• Some VMs can stay down if a host dies
• Can set the % to less than one server's worth of resources, since not all VMs need to restart if a host fails.
• Mistake #5: Forgetting to Prioritize VM restart
• VM restart priority is one of those oft-forgotten settings
• Come into play when Percentage policy is enabled
• Restart policy is per-host
• Per-VM settings must be configured for each VM
• This can create a problem down the road, as VMs may restart in the wrong order
• Mistake #6: Disabling Admission Control
• Many young admins may turn it off and forget about it
• Never disable admission control!!!
• Mistake #7: Not updating Percentage Policy
• Needs to be adjusted as your cluster size changes
• Host failures the cluster tolerates needs no adjusting
• Mistake #8: Buying (the occasional) Big Server
• Host failures the cluster tolerates sets aside the amount of resources the protect every server.
• It must set aside resources equal to your biggest server in the cluster
• Mistake #9: Neglecting Host Isolation Response
• Current recommendation is to leave powered on
• On converged networks you may not want to use powered on
• Heartbeat datastores - Adds redundancy
• Mistake #10: Assuming that Datastore heartbeats Prevent isolation Events
• Master determines the state of the unresponsive host
• Isolation response is triggered by the slave
• Mistake #11: Confusing your ADP with your PDL
• An All Point Down scenario exists when all communication is severed between host and device
• I/O is then queued until a SCSI response code officially reports the link is down
• This can lead to infinite queuing of device I/O
• Permanent device loss scenario exists when the host can see the device target but the target isn't listening
• Lets the host recognize the I/O
• APD is a more common scenario and APD will not trigger vSphere HA
• Look at new settings in 5.0 U1 and 5.1 - Most handy for metro clusters
• Mistake #12: Overdoing Reservations, limits, and Affinities
• HA may not consider these "soft affinities" at failover
• Consider using shares over reservations and limits
• Less impact on DRS and thus HA
• Mistake #13: Considering Using Shares without Considering using Shares
• Shares are only considered during periods of contention
• But settings shares on resource pools can have unexpected results
• Don't treat resource pools like folders
• Mistake #14: Doing memory limits at all
• Don't assign memory limits. Ever.
• Limit memory closest to the application as possible (such as in the SQL app)
• Mistake #15: Thinking you are smarter than DRS
• Not using fully automated mode
• Mistake #16: Not understanding DRS' Equations
• Every 5 minutes a DRS interval is invoked
• Takes into account VM entitlements, host capacity
• Mistake #17: Being too liberal with your migration threshold
• Pri 1 recommendations are mandatory
• Mistake #18: Combining VDI and Server Workloads in the same cluster
• ESXi hosts running VDI workloads tend to experience more load than running server workloads.
• VDI forces DRS to work harder and more often
• Create separate clusters for VDI and everything else
• Mistake #19: Planning on Overcommit
• Over commit creates extra work for the hypervisor
• Assign the right amount of memory to your VMs