Juniper QFX3500

Intro press release is dated February 2011. A pretty cool sales presentation actually contains info on buffer size at slide 25. It has much more information than the published datasheet.

Juniper switches based on Trident+ and Trident2 have some of the buffers dedicated to specific ports with the rest held in a shared pool. Juniper permits allocation rules for shared pool to be adjusted by the user. Here is an example of what that allocation can look like:

show class-of-service shared-buffer

user@switch> show class-of-service shared-buffer
Ingress:
  Total Buffer     :  9360.00 KB   
  Dedicated Buffer :  2158.00 KB  
  Shared Buffer    :  7202.00 KB  
    Lossless          :  648.18 KB   
    Lossless Headroom :  3240.90 KB  
    Lossy             :  3312.92 KB  

  Lossless Headroom Utilization:
  Node Device         Total          Used                  Free
  0                   3240.90 KB     0.00 KB               3240.90 KB  

Egress:
  Total Buffer     :  9360.00 KB   
  Dedicated Buffer :  2704.00 KB  
  Shared Buffer    :  6656.00 KB  
    Lossless          :  3328.00 KB  
    Multicast         :  1264.64 KB  
    Lossy             :  2063.36 KB

Changing the buffer parameters is a disruptive operation. Queuing and dequeuing are handled in the forwarding plane based on parameters the CPU loads into the switch chip. Changing the parameters resets the forwarding plane.

Juniper has an excellent white paper on buffer management that covers several switches that use Trident+ and Trident2 silicon.

This is reinforced by a Q&A on a Juniper Mailing list in 2014.