vCenter 5 slots

[aiea96701]

When I view Advanced Runtime Info, I see the slot calculations.  What do these values mean?

Total slots in cluster:  150

Used slot: 1

Available slots: 75

Failover slots: 75

[a_p_ · Accepted solution]

With the default configuration for HA (High Availability), Admission Control uses a slot based approach to ensure it can protect powered on VMs from host failures. These slots are calculated based on the hosts resources and default slot sizes, or - in case VM based memory or CPU reservations are configured - based on these reservations. For details see e.g. http://www.yellow-bricks.com/vmware-high-availability-deepdiv/

André

[aiea96701]

Thanks. I sorta understand.  So, if I have 150 slots available  in my cluster and 75 are available and 75 for failover, does that mean that if I have a host with 76 VM that 75 will failover to a second host in a powered up state and one will not?

[a_p_]

Not exactly. The Slots are calculated based on the host's resources with either default values or - in case of reservations - based on them. Depending on the resource configuration of a VM, it could consume 1 or more slots. A VM with e.g. 4 GB memory would use approximately 17 slots, if the memory slot size is 256MB (i.e. 4GB / 256MB = 16 slots, plus some overhead).

André

[aiea96701]

Thanks Andre.  So, how do you use this information to manage a hosts failover potential?  Do I calculate each hosts total slots and then compare each to what is available for failover to see what my potential capabilities are to down one host and failover the VMs to other hosts?   How do you do it?

[a_p_]

The number of available slot is basically calculated for each host based on the slot sizes. The - depending on the Admission Control settings and a few other factors - HA calculates the failover capacity. A more detailed explanation of the slot calculation with some examples is covered at vSphere High Availability (HA) Technical Deepdive.

André

[ChopChe]

somewhat complicated but I have an idea of what is going on.just have to chew on each of the various options to determine what is best for us