Dell offers an add-on hardware card for some of their servers that provides a poor man's RAID1 between two SD cards (one card gets all the reads until it dies, writes are mirrored) for booting a simple OS that has very little write load to the OS storage (ie ESXi) - see here (warning: PDF link).
It's great for running a diskless VM host without needing to boot from SAN or worry about a single little cheap flash failure from taking out a host - but it's very much proprietary, to the point that it's integrated to the BIOS of the systems that support it.
Are there any other solutions similar to this out there, offered by server hardware vendors or otherwise (I'm imagining a custom USB flash reader with integrated RAID1?), that allow redundancy between two cheap little chunks of flash storage, hopefully with better compatibility than "a couple specific Dell servers"?
There is this: http://www.idotpc.com/thestore/pc/viewPrd.asp?idproduct=918
It only supports one SD card, but many motherboards have built-in RAID 1 support.
I've had some experience with flash drives and ESXi, and mirroring is definitely to be recommended.
Well I can see that thread is almost 4 years old but ...
Check this http://www8.hp.com/cz/cs/products/flash-media/product-detail.html?oid=6339687
and this http://h20566.www2.hpe.com/hpsc/doc/public/display?sp4ts.oid=4030997&docId=emr_na-c04630357&docLocale=en_US
Time to raise the dead....
FX3S RAID-on-Chip USB Dongle
https://www.cypress.com/products/ez-usb-fx3s
They list a kit, but haven't tried one, so not sure of the usefulness.