Although the switch reserves some buffer space to ensure
a minimum memory allocation for ports and queues, you can configure
how the system uses the rest of the buffer space to optimize the buffer
allocation for your particular mix of network traffic. The global
shared buffer pool is memory space that all of the ports on the switch
share dynamically as they need buffers. You can allocate global shared
memory space to different types of ingress and egress buffers to better
support different mixes of network traffic.
CAUTION:
Changing the buffer configuration is a disruptive event.
Traffic stops on all ports until buffer reprogramming
is complete.
Use the default shared buffer settings (for a network with a
balanced mix of lossless, best-effort, and multicast traffic) or one
of the recommended shared buffer configurations for your mix of network
traffic (mostly best-effort unicast traffic, mostly best-effort traffic
on links enabled for Ethernet PAUSE, mostly multicast traffic, or
mostly lossless traffic). Either the default configuration or one
of the recommended configurations provides a buffer allocation that
satisfies the needs of most networks.
After starting from one of the recommended configurations, you
can fine-tune the shared buffer settings, but do so with caution to
prevent traffic loss due to buffer misconfiguration.
You can configure the percentage of available (user-configurable)
buffer space allocated to the global shared buffers. Any space that
you do not allocate to the global shared buffer pool is added to the
dedicated buffer pool. The default configuration allocates 100 percent
of the available buffer space to the global shared buffers.
You can partition the ingress and egress shared buffer pools
to allocate more buffers to the types of traffic your network predominantly
carries, and fewer buffers to other traffic. From the buffer space
allocated to the ingress shared buffer pool, you can allocate space
to:
Lossless buffers—Percentage of shared buffer pool
for all lossless ingress traffic. The minimum value for the lossless
buffers is 5 percent.
-
Lossless headroom buffers—Percentage of shared buffer pool for packets
received while a pause is asserted. If Ethernet PAUSE is configured on a
port or if priority-based flow control (PFC) is configured on priorities on
a port, when the port sends a pause message to the connected peer, the port
uses the headroom buffers to store the packets that arrive between the time
the port sends the pause message and the time the last packet arrives after
the peer pauses traffic. The minimum value for the lossless headroom buffers
is 0 (zero) percent. (Lossless headroom buffers are the only buffers that
can have a minimum value of less than 5 percent.)
Note:
On a QFX Virtual Chassis and an EX4600/EX4650 Virtual Chassis, the
minimum value for the lossless headroom buffer is 3 percent.
Lossy buffers—Percentage of shared buffer pool for
all best-effort ingress traffic (best-effort unicast, multidestination,
and strict-high priority traffic). The minimum value for the lossy
buffers is 5 percent.
The combined percentage values of the ingress lossless, lossless
headroom, and lossy buffer partitions must total exactly 100 percent.
If the buffer percentages total more than 100 percent or less
than 100 percent, the switch returns a commit error. All ingress
buffer partitions must be explicitly configured, even when the lossless
headroom buffer partition has a value of 0 (zero) percent.
From the buffer space allocated to the egress shared buffer
pool, you can allocate space to:
Lossless buffers—Percentage of shared buffer pool
for all lossless egress queues. The minimum value for the lossless
buffers is 5 percent.
Lossy buffers—Percentage of shared buffer pool for
all best-effort egress queues (best-effort unicast and strict-high
priority queues). The minimum value for the lossy buffers is 5 percent.
Multicast buffers—Percentage of shared buffer pool
for all multidestination (multicast, broadcast, and destination lookup
fail) egress queues. The minimum value for the multicast buffers is
5 percent.
The combined percentage values of the egress lossless, lossy,
and multicast buffer partitions must total exactly 100 percent.
If the buffer percentages total more than 100 percent or less
than 100 percent, the switch returns a commit error. All egress
buffer partitions must be explicitly configured and must have a value
of at least 5 percent.
To configure the shared buffer allocation and partitioning
using the CLI:
