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 trac classes while ensuring lossless delivery of
storage trac with best-eort for LAN trac and latency-sensitive scheduling of service trac.
• 802.1Qbb — Priority ow control
• 802.1Qaz — Enhanced transmission selection
• 802.1Qau — Congestion notication
• Data center bridging exchange protocol
DCB enables the convergence of LAN and SAN trac 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 trac, while transmitting other trac
classes that perform better without ow control (see Priority ow control).
Enhanced
transmission
selection (ETS)
Assign bandwidth to 802.1p CoS-based trac classes. Use ETS to increase preferred trac-class throughput
during network congestion (see Enhanced transmission selection).
Data center bridging
exchange protocol
(DCBX)
Congure the DCBX protocol used by DCB neighbors to discover and exchange conguration information for plug-
and-play capability (see Data center bridging eXchange).
Internet small
computer system
interface (iSCSI)
Use iSCSI auto-conguration and detection of storage devices, monitor iSCSI sessions, and apply QoS policies on
iSCSI trac (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-specic trac 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 trac class, it sends a pause frame for the priority trac to the transmitting device. In this way,
PFC ensures that specied priority trac 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 trac on a link,
as performed by the 802.3x pause mechanism, PFC pauses trac for 802.1p trac types. For example, when LAN trac congestion
occurs on an interface, PFC ensures lossless ows of storage and server trac while allowing for lossy best-eort transmission of other
trac.
PFC handles trac congestion by pausing prioritized dot1p trac on an ingress interface and allowing other dot1p trac best-eort, lossy
data transmission.
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