User`s guide

192 XgOS User’s Guide September 2014
Note The SAN QoS feature set uses vHBAs (not vNICs) and is different from
network QoS. See “SAN QoS for vHBAs” on page 209.
Network QoS assigns the amount of bandwidth and burst size to a given vNIC. The
burst size is the amount of buffering retained for when traffic arrives in bursts
during congestion.
Bandwidth
Guaranteed bandwidth on vNICs is supported through the CIR and PIR values:
CIR—Committed Information Rate. The amount of bandwidth guaranteed to the
vNIC. The CIR is best effort. There is no rate restriction (imposed limit) over the
bandwidth usage.
PIR—Peak Information Rate. The amount of best effort bandwidth
(not guaranteed) for the vNIC to consume as resources become available. By
default, the PIR is the maximum-possible limit of the physical I/O card.
CIR and PIR are specified in Kilobits per second by default. Through software, you
can change the units by using the abbreviations m, g, and k for Mbps, Gbps, and
Kbps respectively.
When implementing Network QoS, due to traffic management overhead, to get
accurate CIR (within 5% range), the sum of all CIRs on an Ethernet link must be less
than 90% of the total link speed. For example CIR1=200 mbps, CIR2=600 mbps, and
CIR3=100 mbps on a 1 Gbps link. Total link speeds can be either 1 Gbps on a 10-Port
GE link, or 10 Gbps on the 10 GE link.
Burst Size
Guaranteed bandwidth during traffic bursts or network congestion is supported
through CBS and PBS values:
CBS—Committed Burst Size. The amount of data committed to be sent in one
transaction.
PBS—Peak Burst Size. The amount of best-effort data that can be sent in one
transaction.
CBS and PBS are specified in bytes by default. through software, you can change the
unit to Gbps and Mbps by using the abbreviations m, g, and k for Mbps, Gbps, and
Kbps respectively.