Hi,
The sfid is the software forwarding infrastructure (sfid).. I haven't been able to find much on the sfid process, just a few references to it as the "software forwarding process"
maybe @parau@juniper.net can explain a bit more about the sfid
What Junos version are your running ? their was a bug in the 12.3R8 junos version it has been resolved in the 12.3R9 version.
On EX4500 or EX4550 switches, the software forwarding infrastructure daemon (sfid) might continuously create core files, causing interruptions in traffic, because packets are erroneously freed twice. A possible trigger is the handling of Layer 2 protocol tunneling packets. [PR/941482: This issue has been resolved.]