Now with the virtualization technologies evolving so rapidly, support for multiple networks on a single host is a must-have with the better network quality. Red Hat felt this need a long time ago and worked their way on top of server products. Basically, Red Hat Enterprise Virtualization allows administrators to configure multiple NICs with the help of bonding for several networks to allow high throughput or high availability.
In this configuration, VM Management or host storage access (iSCSI) can be used for connecting virtual machines on different networks. This configuration looks great but the only bottleneck that comes up is at the host level. One can easily imagine a case where a single network is hogging the outgoing link (e.g. during a migration storm where many virtual machines are being migrated out from the host simultaneously or when there is an attacker VM). The consequences of such cases can include things like lost connectivity to the management engine or lost storage for the host.
With the new version being released, Red Hat Enterprise Virtualization 3.6 introduced a new feature called Host Network QOS to solve the above mentioned challenge and improve the network quality. Because Red Hat Enterprise Virtualization is co-engineered with Red Hat Enterprise Linux 7, virtualization administrators can leverage a plethora of network QOS algorithms called qdiscs – queueing disciplines. The administrator has options and can configure the algorithm on the host NICs.
RHEL 7 embedded the HFSC (hierarchical fair service curve) which allows the administrator to ensure both bandwidth and latency with relatively low performance overhead.
Using HFSC, the administrator can configure a few invariants on the egress traffic including:
- Link sharing. Ensure that a certain class of traffic will not exceed a certain share of the bandwidth during times where there is contention on the NIC.
- Real Time. Allow bursts of traffic to temporarily breach the link share, in order to ensure lower latency.
- Upper limit. A hard upper limit on the egress traffic.