Administrator Guide

Figure 27. Illustration of Trac Congestion
The system supports loading two DCB_Cong les:
• FCoE converged trac with priority 3.
• iSCSI storage trac with priority 4.
In the Dell Networking OS, PFC is implemented as follows:
• PFC is supported on specied 802.1p priority trac (dot1p 0 to 7) and is congured per interface. However, only two lossless queues
are supported on an interface: one for Fibre Channel over Ethernet (FCoE) converged trac and one for Internet Small Computer
System Interface (iSCSI) storage trac. Congure the same lossless queues on all ports.
• PFC supports buering to receive data that continues to arrive on an interface while the remote system reacts to the PFC operation.
• PFC uses DCB MIB IEEE 802.1azd2.5 and PFC MIB IEEE 802.1bb-d2.2.
• A dynamic threshold handles intermittent trac bursts and varies based on the number of PFC priorities contending for buers, while a
static threshold places an upper limit on the transmit time of a queue after receiving a message to pause a specied priority. PFC trac
is paused only after surpassing both static and dynamic thresholds for the priority specied for the port.
• By default, PFC is enabled when you enable DCB. If you have not loaded FCoE_DCB_Cong and iSCSI_DCB_Cong, DCB is disabled.
When you enable DCB globally, you cannot simultaneously enable link-level ow control.
• Buer space is allocated and de-allocated only when you congure a PFC priority on the port.
Enhanced Transmission Selection
Enhanced transmission selection (ETS) supports optimized bandwidth allocation between trac types in multiprotocol (Ethernet, FCoE,
SCSI) links.
ETS allows you to divide trac according to its 802.1p priority into dierent priority groups (trac classes) and congure bandwidth
allocation and queue scheduling for each group to ensure that each trac type is correctly prioritized and receives its required bandwidth.
For example, you can prioritize low-latency storage or server cluster trac in a trac class to receive more bandwidth and restrict best-
eort LAN trac assigned to a dierent trac class.
NOTE
: Use the following command to enable etsacl: cam-acl l2acl 2 ipv4acl 2 ipv6acl 0 ipv4qos 0 l2qos 0
l2pt 0 ipmacacl 0 vman-qos 0 fcoeacl 2 etsacl 3. After executing this command, you must save the
conguration and then reload the system.
The following gure shows how ETS allows you to allocate bandwidth when dierent trac types are classed according to 802.1p priority
and mapped to priority groups.
254
Data Center Bridging (DCB)