There are other varients of this switch with different port configurations but a heart of Trident 3. QFX5120-48Y and QFX5120-32C. There is a family data sheet.
Lifting a paragraph from the data sheet to highlight buffer characteristics:
Intelligent buffer management: The QFX5120 features a total of 32 MB of shared buffers. While 25% of the total buffer space is dedicated, the rest is shared among all ports and is user-configurable. The intelligent buffer mechanism in the QFX5120 effectively absorbs traffic bursts while providing deterministic performance, significantly increasing performance over static allocation.