Hi,
we have 10 Hosts in a cluster
I know one host acts as master and rest all hosts are acts as a slaves. Its do polling.
1. How host became a master ? what resources should have to qualify a master?
2. How often this polling will happen?
3. we have 10 hosts in cluster and there are no vms in any of Hosts all are having same resources in this case which host should be a master?
Please download availability guide from following URL
https://www.vmware.com/support/pubs/vsphere-esxi-vcenter-server-6-pubs.html
This guide has detailed description about vSphere HA, architecture and Election process. Your question mainly is about who becomes master among 10 hosts that you have.
Depends upon how you being
Let's say you have created a cluster and enabled HA.
Now if you start dragging and dropping your hosts one by one into this cluster, the first host enters the cluster becomes master.
But let's say you have cretaed a cluster and not enabled vSphere HA yet, made those 10 hosts member of the cluster and now enabling HA.
in this case, Election process will elect one of the host master purely on the basis of following two criteria
1) highest No. of Datastores visible to host, let's say one of the host is reporting that it has 5 datastore are visible and rest of the 9 hosts in your cluster has 4 datastore visible, then the one with highest no of datastore becomes the master, but this criteria might fail if there multiple hosts with same number of datastore visible and that's the highest
2) in this case, second criteria of election is MOID of all this hosts, each host has got their Managed Obect ID number (MOID) which will be compared lexically and lexically highest number will become master..
I would recommend going through availability guide and you will find answers that you are seeking and much more.
If you want to know more you should take a look at Duncan's blog:
http://www.yellow-bricks.com/vmware-high-availability-deepdiv/
And if you still want to know more you might even want to look at Duncan's and Frank's book:
Although there might be a new version on the way ![]()
Tim
In Lehman Term
1. How host became a master ? what resources should have to qualify a master - election process based on some values whoever win will act as master.
2. How often this polling will happen? - when isolation happen or master goes down.
3. we have 10 hosts in cluster and there are no vms in any of Hosts all are having same resources in this case which host should be a master? - its just a election with (host greatest number of datastores wins and MOID-lexically-highest Managed Object ID)
There is complete book on HA & DRS Deepdive
1. what happen If vcenter server down? Will HA work
2. Suppose all hosts powered off due to power outage issue. One server quickly booted in this case all the VM's are restating to this host?
1. vCenter is just used to configure HA. Once configured the HA functionality is completly done by the hosts without the vCenter. So yes, it will work.
2. Yes, the first server that comes up again will become the master and will start the VMs.
Hi Tim,
If I have 10 hosts. All are power down and one host booted quickly all vm's form all hosts are restarted to single host which is booted first? If there is no resources what happen? Once other hosts back can again restart back to same host?
Hi,
depends how your admission control is configured.
When it's disabled your one host will power up as many VMs as it's able to. The host only needs little ressources for the VM overhead to boot up the VM.
If you don't work with resverations / admission control, your hosts will most likely start more VMs than he can handle, which results in a massive performance impact for the VMs.
HA is like "a crippled running VM performs better than a crashed shutdown VM" ![]()
