Scott Lowe asked a great question on his blog today – Why does XenSource tout having a 64-bit hypervisor? I mean really, what does it give them that VMware doesn’t already have? More host memory support? No. VMware supports 256 GB and XenSource supports 128 GB. More guest memory? No. VMware supports 64 GB and XenSource supports 32 GB. More guest support? No. VMware supports more 64-bit guests than XenSource does. VMware was also the first virtualization vendor with 64-bit guest support. So what are the benefits of the 64-bit hypervisor that XenSource is touting.
I think Keith Adams from VMware told it best on why VMware doesn’t need to go 64-bit in the hypervisor.
I’ve worked in VMware’s virtual machine monitor group since 2000. I’m part of the three-person team who initially brought up 64-bit VMs on AMD hardware before SVM in 2004, and I am the one person team who brought up 64-bit VMs on Intel hardware with VT in 2005.
Our “hypervisor,” the vmkernel, is indeed 32-bit in ESX 3i. However, we make a distinction between our “monitor” and our “hypervisor” that is unfamiliar to Xen folks. Our “monitor” runs at CPL-0 on the bare metal, but is instanced; there is one monitor per VM. The monitor is what actually emulates the CPU, constructs shadow pagetables, programs VT/SVM hardware if appropriate, etc.
Our monitor has been 64-bit (on capable hardware) since 2004. Since the CPU-facing part of the software is 64-bit, it greatly reduces the pressure on us to move the vmkernel to 64-bit. Our customers understand this. When Xen Source sales people try to sell Xen by saying “Xen == 64-bit == new hotness, VMware == 32-bit == old n’ busted”, our customers are right to make fun of them on their blogs, IMHO.
So there you have it. Finally someone called XenSource out on more of their rhetoric. I’m sure I’ll get a bunch of the XenSource fans flaming me on my blog too just like they did to Scott. That’s fine. Just make sure you come with facts this time and not more rants.
DISCLAIMER: These thoughts are my own and are not reflective of my company or anyone or anything else on planet earth.
