Introduced in March 2015. This is not merchant silicon. Packet memory is external to the switch chip. This switch is (your pick)
A detailed architecture paper
Thanks to Rafal Jan Szarecki from Juniper wrote me in August 2015 with this info:
I suspect this is the same information that is on page 4 of the architecture paper cited above. At 100 Gb/s, 100 mS of buffer is 1250 MBytes. The switch data sheet says about queuing architecture:
Juniper has a blog post that explains in some detail how their VoQ works but does not explain queue size management.
The main theme for this page is How much buffer is there for a single flow? We would need to know the switch policies for dynamic buffer assignment. If the switch does not have dynamic buffers, the result will be disappointing. 100 output ports and 8 queues per port, would mean 100 x 8 = 800 port-queues. If 12 ports are sharing 4 GBytes and there are 800 port-queues per input port, there is on average about a 0.5 Mbyte per queue.
Juniper does not use fixed allocations. An extract from their 890 page Traffic Management Feature Guide explains the details. Ports are permitted to claim up to 100 mS of buffer space as long as the 4 GByte pool remains below 90 percent full. The limit is on the total across all queues on each port. But queue allocation shares are adjustable and it is possible to put the entire allocation into the best effort queue. So the packet queue sizes are 1.25 GB for 100 Gb/s ports, 125 MB for 10 Gb/s ports.