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Why would you do anything else for your sysop/sysadmin?
You need at least 10 sysop/sysadmin to achieve anything close to that SLA, with a sustainable rota. Contrary to the parent posters who believe it can be done with THE right guy.
And keep in mind, 20 minute response doesn't mean you fix the problem in 20 minutes, it means you respond in 20 minutes to the callout.
I think you're victim of an easy-going startup culture.
I’ve been oncall for escalations for like 15 years. That’s miserable enough, IMO frontline guys need fixed schedules and rotation if the volume is high.
I definitely cast my perspective on this and apologize if I came on too strong,