Vsphere Ha Slot Size Calculation
For a long time I have been sizing vSphere clusters for customers and I am regularly asked how I work out the overcommitment ratio and calculate the suitable percentage of cluster resources to reserve for HA.
- Vsphere Ha Slot Size Calculation Chart
- Vsphere Ha Slot Size Calculation Calculator
- Vsphere Ha Slot Size Calculation Formula
This calculator is focused on Virtual Server clusters, for VDI solutions I recommend the VDI Calculator by @andreleibovici.
This calculator allows this to be done quickly and easily while giving advice as to the availability level recommended for the cluster based on its size.
All you need to do is enter the follow details into the Yellow fields.
1. The Number of ESXi hosts
2. The total CPU sockets per host
3. Ghz per Core
4. Physical Cores per CPU Socket (Not Hyper-threads)
5. Total RAM per host
6. Total number of VMs
7. The Desired Availability Level (N+x)
Next enter the total number of vCPUs and vRAM assigned (or expected to be) assigned to VMs in the cluster.
VSphere HA slot sizes are used to calculate the number of VMs that can be powered on in an HA cluster with “Host failures cluster tolerates” selected.The slots size is calculated based on the size of reservations on the VMs in the cluster. Vsphere 5 Ha Slot Calculation, craps traner info, usa online blackjack for real money, allroundmarin poker 430 gebraucht. HA uses the highest CPU reservation of any given VM and the highest memory reservation of any given VM. If VM1 has 2GHZ and 1024GB reserved and VM2 has 1GHZ and 2048GB reserved the slot size for memory will be 2048MB+memory overhead and the slot size for CPU will be 2GHZ. Now how does HA calculate how many slots are available per host? When implementing the Cisco Nexus 1000v, High Availability (HA) Slot Sizes can be affected on your vSphere Cluster. HA slot sizes are used to calculate failover capacity for HA when the “Host Failures” HA setting is used. By default the slot size for CPU is the highest reservation of CPU among all VM’s in the cluster (or 256 MHz if no per. Aug 12, 2009 HA uses the highest CPU reservation of any given VM and the highest memory reservation of any given VM. If VM1 has 2GHZ and 1024GB reserved and VM2 has 1GHZ and 2048GB reserved the slot size for memory will be 2048MB+memory overhead and the slot size for CPU will be 2GHZ. Now how does HA calculate how many slots are available per host?
The calculator will then output the following:
1. Total Cluster Resources
This is the total Physical Cores and physical RAM in the cluster.
2. The total Cluster Ghz
Self Explanatory
3. The percentage of Cluster Resources reserved for HA
This is calculated from the availability level specified.
Note: The recommended Availability level is calculator and displayed on the same line as the “Desired Availability Level”.
4. The total available Cluster Resources
This is the total cluster resources, minus the percentage of cluster resources reserved for HA. Note: This is not how vSphere HA calculates available cluster resources. This is a method I use which is conservative and ensures performance does not degrade in the event of the configured availability level.
Finally, it calculates
5. The Overcommitment Ratio for CPU and RAM
This is represented as a ratio, so a result of “1” means no overcommitment.
A result of “4” would be a 4:1 overcommitment or 400%.
The tool then shows a “Rule of Thumb” for overcommitment levels of the vSphere cluster.
Simply modify the number of hosts, Cores per Socket and RAM per host until you have the desired overcommitment levels, then you can Print the sizing chart for your design.
vSphere HA slot sizes are used to calculate the number of VMs that can be powered on in an HA cluster with “Host failures cluster tolerates” selected. The slots size is calculated based on the size of reservations on the VMs in the cluster. HA Admission Control then prevents new VMs being powered on if it would not leave any slots available should a host fail.
The slot size for a cluster can be seen by going to the Summary Page for the cluster and clicking the “Advanced Runtime Info” link in the HA box.
If none of the VMs have CPU or RAM reservations, a default of 256MHz and 0GB is used.
The slots per host is derived by taking the total available CPU/RAM for the host and dividing by the slot size. Some CPU is reserved for the system so it will usually be a little lower than the full amount. So a host with 2xquad-core 2.4GHz CPUs (total 19.2GHz) and no VM CPU or RAM reservations has 73 slots and will only allow 73 VMs to be powered on if the cluster has two hosts and is set to protect against a single host failure.
Vsphere Ha Slot Size Calculation Chart
Obviously this allows a very minimal amount of resource for each VM, so either reservations should be set for each VM, or slots size can be manually adjusted (see the VMware vSphere Availability Guide (pdf) for full details).
Vsphere Ha Slot Size Calculation Calculator
Note that the slot size is used for admission control calculations only. It has no direct effect on the resources available to VMs should an HA event occur.
Vsphere Ha Slot Size Calculation Formula
There is a VMware Knowledgebase article (1010594) which has some details of the difference in VI3 and vSphere 4.x.