> As a manager, how do you determine who deserves a raise and whose hiring was a failure?

IDK, manage? I let go of anyone who is determined to have been a 'hire [that] was a failure.' I also look back and try to figure out what failed in the hiring process. Luckily I haven't had too many failures, because it sucks to let people go - even if they deserve it. Admittedly, I also have never had to hire at the scale of a FAANG.