RAID-1 Memory System

I was thinking these days... IBM has a RAID-5-like memory system on their mainframes, mostly for the reliability (copious amounts of L4$ deal with performance). Having memory sticks arranged in a RAID-1 pattern would allow for twice the random-read bandwidth on L3$ misses at twice the random-write cost on L3$ evictions, but since read/write ratios are usually much larger than 1, it could make sense.

Has anyone ever tried to build this?