Issue 11
© Solarflare Communications 2014
309
Solarflare Server Adapter
User Guide
Typical Virtualization (with SR-IOV)
In emerging SR-IOV solutions a PCIe hardware VF is passed-through to the guest operating system.
A network driver binds directly to this PCIe VF.
Figure 49: Direct Guest Access to NIC Hardware
This approach solves many of the performance limitations of traditional virtualized networking
providing direct access to the network adapter from the guest VM.
However, the major downside of this approach is the guest VM now relies on the physical VF of the
adapter for networking. If this VF changes in anyway then the guest VM completely loses networking
access.
For example, this solution makes migration close to impossible to support as both the source and
destination machine must be identical in every respect to the networking adapter. That is, not only
identical at a hardware level (same adapter, same slot) but, also the same VF index must be available
on the identical destination machine. For example, if VF 5 is being used by the VM at the source
machine then for migration to succeed VF 5 must be free at the destination machine. This means
that for migration to be possible VFs cannot be allocated on demand but assigned to fixed VMs
across the complete cluster. Therefore, for deployments with more than a handful of VMs across the
complete cluster this SR-IOV solution prevents the user from migrating VMs.
It is also worth noting that the networking interface in this model is now a vendor supplied driver
and creation/configuration of networking interfaces must be done via this vendor driver and not the
standard KVM network drivers.