Administrator Guide
Managing Hardware Buffer Statistics
The memory management unit (MMU) is 12.2 MB in size. It contains approximately 60,000 cells, each of which is 208 bytes in size. MMU
also has another portion of 3 MB allocated to it. The entire MMU space is shared across a maximum of 104 logical ports to support the
egress admission-control functionality to implement scheduling and shaping on per-port and per-queue levels. Also, the MMU buffer cells
can be used by each port or queue either as a static partition or as a dynamic partition. With dynamic mode, you can specify the
percentage of available buffer that is utilized by a queue. This dynamic partition or block is set to be two-thirds of the available buffers for
all unicast queues and one-fifth of the available buffers for all multicast queues on these platforms.
The maximum number of ports, including fan-out, supported is 104 and the maximum number of queues supported is 21. Analyzing and
evaluating buffer statistics enables monitoring of resources and tuning of allocation of buffers. Max Use count mode provides the
maximum values of counters accumulated over a period of time. Current Use count mode enables you to obtain a snapshot of the
counters, at a particular time, using a triggering utility. The trigger can either be software-based or based on a predetermined threshold
event. Software-based triggers are supported, which are the values derived from the show command output in the Max Use count mode.
In Dell EMC Networking OS Release 9.3(0.0), only the Max Use count mode of operation is supported for the computation of maximum
counter values.
Depending on the buffer space statistical values that you can obtain, you can modify the settings for buffer area to achieve enhanced
reliability and efficiency in the handling of packets. This evaluation and administration of buffer statistics is useful and important in
deployments that experience congestion frequently. The receive buffer must be large enough to save all data that is received when the
system processes a PFC PAUSE frame.
You can use the service-class buffer shared-threshold-weight queue0 ... queue7 number command in Interface
Configuration mode to specify the threshold weight for the shared buffer for each of the queues per port.
1. Create a 10-Gigabit Ethernet interface.
DellEMC(conf)#interface TenGigabitEthernet 1/1/1
2. Configure the threshold weight of the shared buffer for the queues you want. In this example, this setting is configured for queues 5
and 7.
DellEMC(conf-if-te-1/1/1)#Service-class buffer shared-threshold-weight queue5 4 queue7 6
Enabling Buffer Statistics Tracking
You can enable the tracking of statistical values of buffer spaces at a global level. The buffer statistics tracking utility operates in the max
use count mode that enables the collection of maximum values of counters.
To configure the buffer statistics tracking utility, perform the following step:
1. Enable the buffer statistics tracking utility and enter the Buffer Statistics Snapshot configuration mode.
CONFIGURATION mode
DellEMC(conf)#buffer-stats-snapshot
DellEMC(conf)#no disable
Enable this utility to be able to configure the parameters for buffer statistics tracking. By default, buffer statistics tracking is disabled.
2. Enable the buffer statistics tracking utility and enter the Buffer Statistics Snapshot configuration mode.
CONFIGURATION mode
DellEMC(conf)#buffer-stats-snapshot
DellEMC(conf)#no disable
Enable this utility to be able to configure the parameters for buffer statistics tracking. By default, buffer statistics tracking is disabled.
3. To view the buffer statistics tracking resource information depending on the type of buffer information, such as device-level details,
queue-based snapshots, or priority group-level snapshot in the egress and ingress direction of traffic, use show hardware stack-
unit <id> buffer-stats-snapshot unit <id> resource x
EXEC/EXEC Privilege mode
DellEMC#show hardware stack-unit 1 buffer-stats-snapshot unit 3 resource interface all
queue mcast 3
Unit 1 unit: 3 port: 1 (interface Fo 1/144)
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Q# TYPE Q# TOTAL BUFFERED CELLS
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MCAST 3 0
Unit 1 unit: 3 port: 5 (interface Fo 1/148)
688
Quality of Service (QoS)