QoS Ingress Data Buffer Management

Note

This topic does not apply to SLX 9150/Extreme 8520 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.