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vSAN Witness Appliance Sizing

The vSAN witness appliance OVFs are also used for shared witness. When using a vSAN Witness Appliance, the size is dependent on the configurations and this is decided during the deployment process. vSAN Witness Appliance deployment options are hardcoded upon deployment and there is typically no need to modify these.


Compute Requirements

The vSAN Witness Appliance uses a different number of vCPUs depending on the configuration.


Memory Requirements

Memory requirements are dependent on the number of components.


Storage Requirements

- Cache Device Size: Each vSAN Witness Appliance deployment option has a cache device size of 10GB. This is sufficient for each for the maximum of 64,000 components. In a typical vSAN deployment, the cache device must be a Flash/SSD device. Because the vSAN Witness Appliance has virtual disks, the 10GB cache device is configured as a virtual SSD. There is no requirement for this device to reside on a physical flash/SSD device. Traditional spinning drives are sufficient.


- Capacity Device Sizing: First consider that a capacity device can support up to 21,000 components. Also, consider that a vSAN 2 Node Cluster can support a maximum of 27,000 components. Each Witness Component is 16MB, as a result, the largest capacity device that can be used for storing Witness Components is approaching 350GB.


vSAN Witness Appliance Deployment Sizes & Requirements Summary

Dedicated witness

Tiny - Supports up to 10 VMs/750 Witness Components -Typical for 2 Node vSAN deployments

o Compute - 2 vCPUs

o Memory - 8GB vRAM

o ESXi Boot Disk - 12GB Virtual HDD

o Cache Device - 10GB Virtual SSD

o Capacity Device - 15GB Virtual HDD

Medium - Supports up to 500 VMs/21,000 Witness Components - Alternative for 2 Node vSAN deployments with a significant number of components

o Compute - 2 vCPUs

o Memory - 16GB vRAM

o ESXi Boot Disk - 12GB Virtual HDD

o Cache Device - 10GB Virtual SSD

o Capacity Device - 350GB Virtual HDD

Large - Supports over 500 VMs/45,000 Witness Components - Unnecessary for 2 Node vSAN deployments.

o Compute: 2 vCPUs

o Memory - 32 GB vRAM

o ESXi Boot Disk - 12GB Virtual HDD

o Cache Device - 10GB Virtual SSD

o Capacity Devices - 3x350GB Virtual HDD

8GB ESXi Boot Disk*, one 10GB SSD, three 350GB HDDs

Supports a maximum of 45,000 witness components


Shared witness OVA file for vSAN 7 Update 1

An extra-large option is introduced to accommodate the shared witness appliance's increased number of components.

1000 components per 2-node cluster.

Tiny - Supports up to 10 VMs/750 Witness Components o Compute -1 vCPUs o Memory - 8GB vRAM Medium - Supports up to 500 VMs/21,000 Components o Up to 21 clusters 2-node clusters o Compute - 2 vCPUs o Memory - 16GB vRAM

Large - Supports over 500 VMs/ 24,000 Components o Up to 24 clusters 2-node clusters o Compute: 2 vCPUs o Memory - 32 GB vRAM


Extra-large - Supports over 500 VMs/ 64,000 Components

o Up to 64 clusters 2-node clusters o Compute: 6 vCPUs o Memory - 32 GB vRAM


Above information is directly obtained from the VMware blog.


Thank you for reading!


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