We recently started looking at some of the open source solutions such as KVM/QEMU offered by RedHat and Proxmox to replace Microsoft Hyper-V and VMWare vSphere. So far they do appear somewhat feature-full especially for smaller environments. It appears though they do fall short of Enterprise features.
The performance and simplicity were definitely appealing with these solutions. Some of our staff was really into the Linux aspect of them since the Hypervisors have a full Linux shell. Controlling the enviornment easily from a cli was definitely a plus along with the common feel of logfiles and Linux kernel options.
Everything was promising but we got to the point of backing up multi-terabyte VM environments and the flexibility offered by common tools wasn’t working well enough for what we wanted to do. Products such as Veeam really do make it easy for even entry level administrators to use the complex environments.
For now we’ll be sticking with the big boys and keeping a close eye on the developments of Change Block Tracking in libvirt and the user-space tools in the coming year.