Redis is for high frequency cache, disk latencies would slow it too much. Maybe putting something that would normally be evicted to disk could be valid compromise.

another major drawbacks of Redis is that It is single threaded and sync. you need expensive high frequency CPU if you need more performance. something that could benefit from multi core system and if you would want to use disk cache async is a must. single threading also affects scripts running on Redis side, when they execute whole Redis is waiting and is unable to fulfil other requests.

another place for improvement would be proper easier to use HA, and maybe also auto scaling.