2 Encoders per axis ?

Hi all, I have some questions and would like to hear your opinion on retrofit. The retrofit is  on a older Deckel FP4A “another thread”.
Glass scale encoder vs just motor encoder??.     
Is it ok to just have the motor encoder for a system regarding backlash in the system ? ??
Leadshine EL8 or Delta drives with 2 encoder inputs ??Any out there running 2 encoders pr axis ? via EtherCat ?Have a nice day all.

Short answer:
Yes, you can use encoders, even 2 encoders per axis/joint, or an encoder and a glass scale, both wired to Mesa/LinuxCNC,
and
Yes, you can have one encoder (usually the one on the motor shaft) wired to drive and a glass scale wired to Mesa/LinuxCNC
and
Yes, you can have new drives that take step/dir pulses and have their own encoder and add glass scales wired back to Mesa/LinuxCNC
and
Within reason, pretty much however you like/need.
As for backlash, the best and easiest way is the last version from above.

Thank you i didn't know witch direction i would go.. but now i have a idear