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In order to activate a VSAN (witness), I need to make a quote for SSDs needed.
The goal is to buy at least 4 (2 per server) (including 1 in SPARE online per server).
I remind you that a big part of the SAS disk of each of the 2 ESX will be used for the VSAN.
Has VMware validated a list of SSDs for DELL R740?
What capacity (GB) is required for these SSDs?
The goal is to be able to make an estimate.
I hope that the VSAN will allow the execution of a VM regardless of where this VM will be stored in the VSAN, especially in case of failure of one of the 2 ESX, with automatic restart of the VM with the other ESX, thanks to the HA features.
Firstly, just to explain a bit about how vSAN works:
We use (typically) smaller and faster SSDs for cache-tier and then (typically) larger lower performance SSDs for capacity-tier - note that the cache-tier does not contribute any space to the size of the vsanDatastore only the capacity-tier devices.
While having hot-spares on hand is always a good idea, providing enough slack-space that everything can be rebuilt can avoid this being necessary and then replace failed devices when/if this occurs.
Witnesses do not require a physical server to run on and this is a tad wasteful/expensive in my opinion - it sounds like you are planning a 2+1 (DirectConnect) or 1+1+1 (stretched) cluster, if you have some other environment (e.g. ESXi with SAN/NAS) you can run the Witness as a Appliance VM or alternatively host this on the cloud etc.
"Has VMware validated a list of SSDs for DELL R740?"
We do not validate/certify devices just for any specific server - any of our certified devices can be used in ESXi-compatible servers, you can check what is certified here:
(click "Build Your Own based on Certified Components.")
"What capacity (GB) is required for these SSDs?"
It is unclear from what you said whether you are just looking for sizing devices for a Witness or as cache-tier or capacity-tier as the vSAN storage - please clarify this.
Default Witness sizings are like so:
Tiny (10 VMs or fewer)
2 vCPUs, 8GB vRAM
8GB ESXi Boot Disk, one 10GB SSD, one 15GB HDD
Supports a maximum of 750 witness components
Medium (up to 500 VMs)
2 vCPUs, 16GB vRAM
8GB ESXi Boot Disk, one 10GB SSD, one 350GB HDD
Supports a maximum of 21,000 witness components
Large (more than 500 VMs)
2 vCPUs, 32GB vRAM
8GB ESXi Boot Disk, one 10GB SSD, three 350GB HDDs
Supports a maximum of 45,000 witness components