I am in the process of creating a recovery USB to be used in case of our planned QFX VCF upgrade to 18.1R3S10.
I know the process of creating it, mounting USB, using dd etc ...
My question which media image I need to install from Juniper, what is the difference between these two which both available in media downloads section for QFX5100 18.1R3S10:
install-media-qfx-5-18.1R3-S10.4.img (important is the qfx-5) is the image which is recommended if you just use QFX5100 devices in your VCF.
install-media-host-usb-qfx-5e-x86-64-18.1R3-S10.4.img (important is the qfx-5e) is necessary if you need to have a VC with QFX5100 and newer QFX devices, like QFX5110.
You can find more information here:
As you seem to just use QFX5100, then the "qfx-5" image should be your choice.