The 7210 SAS-Sx/S 1/10GE and 7210 SAS-Sx 10/100GE has 4MB of packets buffers and it supports only a single mode of operation, per node MBS pool, in this release. In this mode, the MBS pool is shared across all queues on all ports. In the per node MBS pool mode, each of the 16 egress queues available on a port, is allocated a CBS amount of committed buffers. The remaining amount of buffers is allocated toward the per node MBS pool that is available for sharing among all the queues across all the ports of the node.
The system internal ports, such as internal loopback ports used for mirroring, port loopback with mac-swap, and others, are allocated with some buffers. Some buffers are reserved for system internal use (for example, CPU queues).
The amount of buffers remaining after allocating buffers for system internal use is available for allocation toward MBS buffers for all egress queues and per node MBS pool.
The hardware implements an algorithm to handle requests for allocation of buffers from the MBS pool assuming that not all the ports and queues burst at the same time. This allows some queues to use a larger portion of the buffers when it is available, allowing them to handle larger bursts. At the same time, the algorithm ensures that all the queues get fair share of the buffers, so that the throughput on those ports are not affected. When the hardware receives a packet, before it decides to queue up the packet on the egress queue of the destination port, it determines the discard threshold for the queue based on the oversubscription factor and the total amount of free buffers available at that point of time.
The queue’s discard threshold is higher, if the amount of free buffers available is larger (which indicates other queues on the node have lesser congestion), allowing the queue to absorb larger bursts. The queue’s discard threshold is lower, if there is lesser amount of free buffers available (which indicates that other queues are heavily congested on the node), which results in the packet being dropped. At the same time, algorithm allocates the available free buffers to queues which are using lesser amount of buffers or not using any buffers. This allows equal sharing of available buffers and maintains a good throughput for less congested queues.
The 7210 SAS-Sx/S 1/10GE does not support per-port MBS pool mode and port decommissioning features in this release.
Buffer pools cannot be created or deleted on the 7210 SAS.