As you are planning to get all new hardware and move everything to new hardware you could follow below :
1>Check the compatibility guide and then Get all your new hardware servers which holds good with ESXi 6.5 , below is the link to check compatibility:
VMware Compatibility Guide - Guest/Host Search
2>Once you have supported hardware for 6.5 , complete esxi 6.5 installation
3>If you can these new servers to existing Vcneter , add it and migrate all VM's from old esxi to new esxi ( considering the VM's are on shared storage, which means the storage should be accessible from new esxi hosts well)
4>Once done, you cna remove the existing old esxi hosts from inventory .
If your VC is also on physical machine then first upgrade your VC to 6.5 so that it is capable enough to manage your new esxi hosts .
Check below link that can also help you :
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Hope you are well and apologies for the delay in replying.
We will be moving all of the vm infrastructure over to new hardware, including the management server. As we are moving to 6.5 I believe for the management side it is better at this stage to move to the appliance rather than windows based (what we currently have).
With this in mind is it better to upgrade the current management server to 6.5. Install ESxi (Will this need to be the trail version until the old host is retired for licencing?), Register the host within vsphere, move the VMS, repeat until upgrade complete. After completed migrate the management server over to the new server (what is the best way to do this?)
Or install the appliance on the new hardware first? If so do we have to setup from scratch or is there a migration procedure? Will we need to reregister the old hosts to move the vms/ move onto the new servers?
4 hosts and 33VM's seems an awfully low VM count for 4 hosts.
What licence are you on?
Go with Virtual VCSA, forget a physical management server.
Please refer these best practices. https://kb.vmware.com/s/article/2147686 https://kb.vmware.com/s/article/2147548` Here is my approach to this migration. You can build fresh 6.5 vcenter environment without touching your existing environment. Once your new 6.5 vcenter is ready, build 6.5 hosts on new hardware that you are planning to get. Add these hosts to 6.5 vcenter, make sure same storage and networks are visible to these hosts that are seen by 5.5 hosts. Plan a downtime and take your vms out of inventory from 5.5 host and register them on 6.5 hosts in new vcenter. Power on VMs in new vcenter, once your VMs are online your 5.5 environment is ready for decommission. You can simply write a powercli script to unregister and register vms, but in your case you have only 33 VMs you can do it manually. This is a bit long method, but easy if planned properly. Thank you
Plan a downtime and take your vms out of inventory from 5.5 host and register them on 6.5 hosts in new vcenter.
Before you do this, make very certain you understand the impact this will have on external tools like monitoring, backup, and reporting as they *will* require reconfiguration and may register as effectively new VMs. I'd recommend you read my blog post to get a better understanding of what to expect in this "swing"-style migration.