Slot size vmware, these...
That topic gets trickier because other VM reservations get included in that number.
Andy was a real help recently when I tried to configure a Cisco switch. How are Slots Sized?
If you have 25 CPU slots but only 5 memory slots the amount of available slots for this host will be 5. To begin this post, we need to understand what a slot is. A VMware ESXi cluster needs a way to determine how many resources need to be available in the event of a host failure.
Admission Control Using Host Failures Cluster Tolerates Policy The way that slot size is calculated and used with this admission control policy is shown in an example. This led to a very conservative and restrictive admission control. This is because some virtual machines can take up multiple slots.
ESXi seems to be a slightly different beast when it comes to calculating the host reservations and requires further investigation. Not only must you subtract the host-level resource reservations as exhibited by the Total Capacity metric provided by the Resource Allocation tab of the cluster but you must also subtract HA level reservations remember those 86 slots in the example above for host failure tolerance or percentage of resources as included in the Reserved Capacity metric.
If it is, admission control disallows the operation. This slot calculation gives the cluster a way to reserve the right amount of resources.
If you have not specified a CPU reservation for a virtual machine, it is assigned a default value of 32MHz. Note that if you do this, some of your VMs will require multiple slots to run.
The cluster has one available slot the six slots on H2 and H3 minus the five used slots. If your cluster contains any virtual machines that have much larger reservations than the others, they will distort slot size calculation. The largest host is H1 and if it fails, six slots remain in the cluster, which is sufficient for all five of the powered-on virtual machines.
In other words a slot size is the worst case CPU and Memory reservation scenario in a cluster. What these documents and articles do not tell us is how this slot size translates to the Available Slots as show in the Advanced Runtime Info of vCenter 4. The same calculation is made for the host's memory resource amount.
To avoid this, you can specify an upper bound for the CPU or memory component of the slot size by using the das.
With the Host Failures Cluster Tolerates admission control policy, vSphere HA ensures that a specified number of hosts can fail and sufficient resources remain in the cluster to fail over all the virtual machines from those hosts. If you have 8 hosts with 90 slots in total but 7 hosts each have 10 slots and one host 20 this single host will not be taken into account.
The number of slots available to power on additional virtual machines in the cluster.