QoS Ingress Data Buffer Management

Note

This topic does not apply to SLX 9150, SLX 9250, Extreme 8520, and Extreme 8720 devices.

Buffer management consists of the following.

Packets arrived at ingress are stored in a data buffer (DB).
A DB can be an on-chip buffer (OCB, 128 MB) or external DRAM (up to 8 GB).
Each OCB size is 256 B and external DRAM buffer size is 2 KB.
The Virtual output queue (VOQ) holds packet descriptors, which are lists of buffer descriptors (BD).
The entire packet buffer can be configured for a given VOQ to 1.5 GB for D cards and 2 GB for M cards.
Important
Specifying a value over 1.5 GB for a D card generates an error:
QSizeLimit LC Type -D ifIdx: 0x80000000, slot_id: 1, maxQueueSize: 1536.
The DB and BD pools are managed per-license, as follows:
- Avoid starving high-priority traffic by allocating too many resources to high-rate, low-priority traffic.
- Each VOQ has its own minimum guaranteed BD and DB (10% of the queue size). The default VOQ size is 1 MB.
- The non-guaranteed BD and DB are allocated from a shared pool.

Note

The buffer management feature is supported only on devices based on Extreme 8820, SLX 9740, SLX 9640, and SLX 9540.