Lenovo ThinkSystem NE2552E, Application Manual

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NE2552E Application Guide for ENOS 8.4
Effects on Flow Control
When CEE is off (the default), 802.3x standard flow control is enabled on all switch
ports by default.
When CEE is turned on, standard flow control is disabled on all ports, and in its
place, PFC (see “Priority ‐ Based Flow Control” on page 256 ) is enabled on all ports
for 802.1p priority value 3. This default is chosen because priority value 3 is
commonly used to identify FCoE traffic in a CEE environment and must be
guaranteed lossless behavior. PFC is disabled for all other priority values.
It is recommend that a configuration backup be made prior to turning CEE on or off.
Viewing the configuration file will allow the administrator to manually re ‐ create the
equivalent configuration under the new CEE mode, and will also allow for the
recovery of the prior configuration if necessary.
When CEE is on, PFC can be enabled only on priority value 3 and one other
priority. If flow control is required on additional priorities on any given port,
consider using standard flow control on that port, so that regardless of which
priority traffic becomes congested, a flow control frame is generated.
RoCE and iSCSI
RDMA over Converged Ethernet (RoCE) allows remote direct memory access
(RDMA) over an Ethernet network. RoCE provides direct memory to memory
transfers at the application level without involving the host CPU. Both the
transport processing and the memory translation and placement are performed by
hardware resulting in dramatically lower latency and higher performance. There
are two RoCE versions, RoCEv1 and RoCEv2: RoCEv1 is an Ethernet link layer
protocol and hence allows communication between any two hosts in the same
Ethernet broadcast domain, while RoCEv2 is designed to allow lossless traffic in
the layer 3 network environment.
Internet Small Computer System Interface (iSCSI) is an Internet Protocol (IP) ‐ based
storage networking standard for linking data storage facilities. It provides
block ‐ level access to storage devices by carrying SCSI commands over a TCP/IP
network. iSCSI takes a popular high ‐ performance local storage bus and emulates it
over a wide range of networks, creating a storage area network (SAN). Unlike
some SAN protocols, iSCSI requires no dedicated cabling; it can be run over
existing IP infrastructure. As a result, iSCSI is often seen as a low ‐ cost alternative to
Fibre Channel.
RoCE Requirements
The following are required for implementing RoCE using the switches with ENOS
8.4 software:
 An underlying lossless Ethernet network is required for RoCE traffic only to
avoid systematic packet drops resulting from resource contention within
network switches and adapters.
 CEE must be turned on (see “Turning CEE On or Off” on page 246 ). When CEE is
on, the DCBX, PFC, and ETS features are enabled and configured with default
settings. These features may be reconfigured, but must remain enabled for RoCE
to function.