A few things to add, while considering the options:
1) Networking type - 1/10/20/40Gbps. On fast networks, over 1Gbps, all modes will show a significant result.
2) Transport type:
- SAN - normally, the fastest method. Have to watch out for proper operational procedures, so not to end up with production volumes being auto-mounted. Gives the best results in terms of performance. Requires connectivity straight to the SAN fabric.
- HotAdd - my personal preference. Easy to deploy; allows to scale Proxy VM depending on the workload; storage-agnostic, should you change your backend infrastructure to a different type of storage vendor that may not work with Veeam as efficiently. Usually I see about 10% loss of performance, compared to SAN mode, mostly due to the overhead on running it on top of a Hypervisior. Allows to push traffic through the network different than systems Management one.
- NBD - the worst option, when it comes to performance. Ideally to be used with a Proxy appliance still to allow distributed mode for overall solution and optionally - push traffic over preferred network path instead of going through MGMT network of the hypervisor. Works well for a lower change rate environments, with CBT enabled and not too much changes happening within a reasonable window.
Product Architect @ SingleHop - Veeam Platinum Service Provider
VCAP-DCD, VCAP-DCA, VCP-NV
Veeam Certified Architect