I read some documents and still not be able to find a good understanding whether QFX5110-48S support 1GE copper?
Appreciate any input.
They are supported. Can be figured out via Pathfinder -> Hardware compatibility tool (direct link to the requested information: https://apps.juniper.net/hct/category/#catKey=100001&modelType=All&pf=QFX+Series )
NOTE! It's not supported to have the 1G copper transceivers installed in the same column of ports as the RJ45 locking mechanism on these will get stuck to each other without any way to remove them from the SFP+ ports. Usually I decide that copper transceivers should go into either even or uneven ports - not a mix.