Re: VADP Backup Limitations
NetWorker's implementation of VADP uses underlying APIs from VMware that only support Windows today. This impacts NetWorker ability to support for Linux proxies. That's not to lay blame or accept blame, it's simply to help our users understand why the initial VADP implementation is exclusively weighted to Windows support. We are looking at options other than VMWare API to address market demand for Linux operability.
Changed Block Tracking (CBT) is an interesting discussion. Now that NW 7.6 SP2 has been available for a while we've learned that the market's expectation for this technology has less to do with the block based protection and more to do with consolidataing the changed blocks into an image for single-step recovery. In hind sight this makes sense - reduce the backup window and reduce the recovery window/steps. Still, this is not the use case we deisgned for and it will require engineering work to adjust NetWorker's implementation of CBT to satisfy the recovery use case.
With regard to the number of proxy servers I have more questions than answers. It's puzzling why it appears to take 18 VADP proxy servers to replace a single VCB proxy server, if all other variables are the same - # of VMs, ESX, clusters, etc. We have seen that VADP is inherently more efficient and flexible than VCB, and across the board we're not hearing of proliferation of proxy servers. Keep in mind that NetWorker's VADP implementation does provide for File Level Recovery (Windows) where VCB did not. This means you do have new configuration considerations to support backup/recovery options that weren't relevant with VCB. And certainly backup window and bandwidth are design requirements that can impact the number of proxy servers needed.