In this video, Russ Long reviews some of the issues you may have with interoperability between VSAN and HA. Learn how communication is effected when we utilize both technologies.
- [Instructor] Since many of you probably have a vSAN implementation, let's discuss how HA and vSAN work together. Requirements of this configuration are fairly simple. First, you need to run ESXi version 5.5. No surprises there since the earliest version of ESXi that actually supports vSAN is 5.5. You will need at least three hosts. Now there are some administrators out there who will hem and ha about the two vSAN minimum versus a three vSAN minimum.
This is not a vSAN course, this is about reliability in HA, and for this, I would like you to have at least three hosts. Those of you who aren't familiar or have never tried running vSAN or HA, I would like you to note that vSAN should be enabled first, then configure HA afterwards. This is due to some of the network considerations. Now when we enable HA with vSan, communication changes. We will no longer use the management network for communication between HA agents on the host, but will use the vSAN storage network.
If vSAN is disabled, then communication will return to the management network. HA agent traffic, in my experience, has not caused congestion issues over the storage network. At least not that I have seen. I've heard some anecdotal evidence that it may. As an administrator, I'd at least give the possibility some thought. Now when you enable vSAN, any changes to the vSAN network are not relaid to HA. So to make changes to the vSAN network when HA is enabled, you must first disable host monitoring, then make your changes, then re-enable host monitoring for communication to be assured.
So here are some changes. As we discussed in our heart beating lesson, we are not allowed to use any data store for heart beating that is participating in vSAN. Another small change is we will no longer be confirming host isolation over the management network but the vSAN storage network. This falls in line with the networking changes we discussed earlier. All HA agent traffics has been moved to the vSAN storage network. Now, there is a limitation when we have HA and vSAN working together.
And what it boils down to is this: your vSAN tolerances should be greater than or equal to our HA tolerances. If we have our HA tolerance set to two, our vSAN tolerances should be two or greater.
Note: This course will also help you prepare for the Configure and Administer vSphere Availability Solutions domain of the VMware Certified Professional – Data Center Virtualization exam. View the exam blueprint at https://mylearn.vmware.com/mgrReg/plan.cfm?plan=64180&ui=www_cert.
- How vSphere High Availability works
- The basics of clusters
- Understanding failure types and failure response
- Monitoring HA virtual machines and appliances
- Using heartbeats
- Creating and configuring clusters
- Configuring admission control
- Best practices: Networking, interoperability, and cluster monitoring