Reference Guide

Converged data center services
OS10 supports converged data center services, including IEEE 802.1 data center bridging (DCB) extensions to classic Ethernet. DCB
provides I/O consolidation in a data center network. Each network device carries multiple trac classes while ensuring lossless delivery of
storage trac with best-eort for LAN trac and latency-sensitive scheduling of service trac.
• 802.1Qbb — Priority ow control
• 802.1Qaz — Enhanced transmission selection
• 802.1Qau — Congestion notication
• Data center bridging exchange protocol
DCB enables the convergence of LAN and SAN trac over a shared physical network in end-to-end links from servers to storage devices.
In a converged network, all server, storage, and networking devices are DCB-enabled. DCB supports bre channel over Ethernet (FCoE)
and iSCSI transmission of storage data. DCB is not supported on interfaces with link-level ow control (LLFC) enabled.
Priority ow control
(PFC)
Use priority-based ow control to ensure lossless transmission of storage trac, while transmitting other trac
classes that perform better without ow control (see Priority ow control).
Enhanced
transmission
selection (ETS)
Assign bandwidth to 802.1p CoS-based trac classes. Use ETS to increase preferred trac-class throughput
during network congestion (see Enhanced transmission selection).
Data center bridging
exchange protocol
(DCBX)
Congure the DCBX protocol used by DCB neighbors to discover and exchange conguration information for plug-
and-play capability (see Data center bridging eXchange).
Internet small
computer system
interface (iSCSI)
Use iSCSI auto-conguration and detection of storage devices, monitor iSCSI sessions, and apply QoS policies on
iSCSI trac (see Internet small computer system interface).
Priority ow control
In a converged data-center network, to ensure that no frames are lost due to congestion, use priority ow control (PFC). PFC uses the
802.1p priority in the Ethernet header to pause priority-specic trac sent from a transmitting device. The 802.1p priority is also known as
the class of service (CoS) or dot1p priority value.
When PFC detects congestion of a dot1p trac class, it sends a pause frame for the priority trac to the transmitting device. In this way,
PFC ensures that specied priority trac is not dropped by the switch.
PFC enhances the existing 802.3x pause capability to enable ow control based on 802.1p priorities. Instead of stopping all trac on a link,
as performed by the 802.3x pause mechanism, PFC pauses trac for 802.1p trac types. For example, when LAN trac congestion
occurs on an interface, PFC ensures lossless ows of storage and server trac while allowing for lossy best-eort transmission of other
trac.
PFC handles trac congestion by pausing prioritized dot1p trac on an ingress interface and allowing other dot1p trac best-eort, lossy
data transmission.
11
Converged data center services 621