A colleague had a question around the maximum amount of host failures HA could take. The availability guide states the following:
The maximum Configured Failover Capacity that you can set is four. Each cluster has up to five primary hosts and if all fail simultaneously, failover of all hosts might not be successful.
However, when you select the “Percentage” admission control policy you can set it to 50% even when you have 32 hosts in a cluster. That means that the amount of failover capacity being reserved equals 16 hosts.
Although this is fully supported but there is a caveat of course. The amount of primary nodes is still limited to five. Even if you have the ability to reserve over 5 hosts as spare capacity that does not guarantee a restart. If, for what ever reason, half of your 32 hosts cluster fails and those 5 primaries happen to be part of the failed hosts your VMs will not restart. (One of the primary nodes coordinates the fail-over!) Although the “percentage” option enables you to save additional spare capacity there’s always the chance all primaries fail.
All in all, I still believe the Percentage admission control policy provides you more flexibility than any other admission control policy.
25% is the commonly suggested figure, would this round up to 33# for a 3-host cluster?? Is another percentage better for such a small cluster??
Thank you, Tom
I suggest what ever the customer requires 🙂
N+1 -> convert to percentage based on amount of host
N+2 -> ….