Saturday, February 6, 2016

Virtual San Stretched Clusters

Virtual San Stretched Clusters

Things to know


Virtual San Stretched Clusters were introduced in vSphere 6.0.1. The are intended for customers
that want to avoid disasters.


2 active/active sites with equal number of esxi hosts. The third site hosts the VSAN esxi appliance.

Minimum number of hosts:

3. 1+1+1

Maximum number of hosts:

31. 15 + 15 +1


Note: The witness host should NOT be in the VSAN Cluster.

The witness appliance:

The witness appliance can be downloaded from and installed via ovf.


How it works:

Virtual machines will have one copy of the data on each site, with the witness located in the witness host. FTT is the only configuration supported. FTT2 and FTT3 are NOT supported. If the vm needs to be restarted, HA will take over. Notice that the creation of the sites is performed with the web client.

Things to know:

All-flash VSAN and Hybrid Virtual Sans are supported.

The VSAN file system needs to be V2.

SMP-FTT is NOT supported.

Read locality is NOT spread across sites. They are performed in the "preferred" site.

Both the Windows and Linux vCenters are supported.

Network latency between sites CAN'T exceed 5 msec (2.5 in each direction).

Maximum number of Fault Domains is 3.

The VSAN witness uses 2 vcpus and 8gbs of RAM. 

3 choices are available: Tiny, Normal and Large. They support 750, 22000 and 45000 witness components.

VMware recomends not running above 50% consumption to allow all the vms to run on the second site in the event of a failure.

H.A. needs two isolation addresses, one x site. (das.isolationaddress 0 and 1)

H.A. should use "Reserved failover CPU and Memory capacity" = 50%

H.A. should have VMCP disabled.

H.A. should have the "Host Isolation" setting to "Power off and restart vm"

DRS should be enabled with "soft" rules so that vms vmotion within a fault domain.

DRS should be enabled with two VM-Host groups.


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