There are many great benefits to hyper-converged technologies, the underside is that there can be some mis-understandings from the community about how the product and architecture actually works.
Specifically there has been some discussion of late about the I/O path through the hypervisor and there appears to be a knowledge gap of how this actually works.
Let me take this opportunity to educate and clarify….
There was some mis-information recently posted stating that Nutanix extends the I/O path, forcing VM I/O to go through the hypervisor twice; being the first time when it leaves the guest VM and the second time when it leaves the Nutanix Controller VM.
While it is true that the VM traffic goes through a VSA, it is incorrect to say that VM traffic goes via the hypervisor to access disk devices twice. Nutanix uses VMDirectPath I/O pass-through to allow direct access to disk controllers and all disk devices, removing the I/O transposition. The hypervisor is actually oblivious of the SSD/HDD devices. This allows the native controller drivers to be used, avoiding any bugs that may be introduced by non-standard or custom written drivers for the hypervisor. The picture below demonstrates the simplicity of the Nutanix data path with VMDirectPath I/O.
The picture above also demonstrates that all the IO is served via the CVM, where most Read IOs are actually served from RAM providing microsecond read latency experience that Nutanix customers love; whilst unfortunately VSAN is not in the enviable position to provide such benefit because it relies solely on a single flash device per disk group per server. (read this test that generated half million IOPs with single block)
Again, most unfortunate are the claims against the VSA approach because when you look deeper at how VSAN is able to offer basic table-stakes enterprise data services you quickly notice that this story is flawed. To deliver simple day-to-day services like compression, de-duplication and encryption VSAN needs to rely on 3rd party external VSAs that are not maintained by VMware and therefore do not have any type of code inspection to ensure security and reliability.
Such these services also run in hypervisor user space and also require additional resources such as RAM and CPU for the applications and the multiple virtual machines. Furthermore, that also dismantle the ‘single throat to choke’ for support story.
I’m happy to be able to set the story straight with the VSA approach. I believe that the benefits of having an integrated and unified data services aid in providing a robust, secure and future-proof platform that at the end of the day benefits customers.
This article was first published by Andre Leibovici (@andreleibovici) at myvirtualcloud.net.