VMware recommends using vSAN ReadyNodes when running vSAN in production. Doing so simplifies the life of the administrator, who doesn't have to ensure all components in the server are certified, have the right firmware, etc. VMware provides the following link where users can find the different vSAN ready node options from various OEMs.
A customer might have specific requirements which mean that an off-the-shelf vSAN ready node isn't suitable. In such circumstances, customers are allowed to modify a vSAN ReadyNode, which could be done either by the OEM or the customer themselves. Biswapati Bhattacharjee, vSAN Product Manager, has provided this excellent blog post explaining how a vSAN ReadyNode can be modified and still be certified:
Worth mentioning is that customers must buy the server labeled as a vSAN ReadyNode from the OEM to be allowed to modify it. That means the chassis doesn't become a vSAN ReadyNode if a customer builds it from individual components, even if the parts are the exact same as in a vSAN ReadyNode. There are some cases where this becomes relevant. SAS expanders are, for instance, only supported on certified vSAN ReadyNodes, not when the server is built from individual components. If you need to use a SAS Expander in your chassis, you must buy a server labeled as a vSAN ReadyNode from the OEM and modify it if necessary.
High level, these are the changes you are allowed to make on a vSAN ReadyNode:
- CPU: You are allowed to change the CPU of the server if the core count and CPU clock speed are better than the vSAN ReadyNode. You are not allowed to change the CPU generation though.
- Memory: You are allowed to increase, but not reduce, the amount of memory in a server.
- vSAN Cache and Capacity disks: You can change the vSAN disks to the same or better performance and endurance class. You can also change the number of disks and disk groups. The disk protocol must also be the same. You CAN'T swap NVMe to SAS or vice versa.
- Storage Controller: You are NOT allowed to change the storage controller, it must stay the same as the original vSAN ReadyNode. You are allowed to add additional controllers of the same type though.
- SAS Expander: You are NOT allowed to change SAS expander in the server chassis.
- Network Interface Cards: You can add more or change Nics as long as they are certified for ESXi and of the same or better performance than the Nics in the vSAN ReadyNode.
- Boot Device: You can change the ESXi boot to any other method supported for ESXi. The boot devices must always be on a separate controller from vSAN though.