Is it reasonable to make a RAID-1 array with a ram disk and a physical disk to maximize read performance and protect data?

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http://serverfault.com – In one of the answers on SO (I forgot which one) I've seen a suggestion to make a RAID-1 array composed of a RAM disk and a physical partition. By adding the physical partition with --write-mostly and enabling --write-behind the system should read everything instantly from the RAM disk but still save all data to the physical partition so that the data are preserved and the RAID array can be assembled again after reboot. Is such a setup reasonable? Will it perform any better in some scenario than having just the physical partition and perhaps tweaking the kernel to favor disk cache (swappines (HowTos)