There was link to the paper [1] on the list, where authors investigate possibility of fault-tolerant btree using shadowing techniques, which allows writable snapshots. Probably it will be of interest to you. It's on my list for testing, but i haven't any benchmarks done with described things yet.
[1]http://www.cs.tau.ac.il/~ohadrode/papers/btree_TOS.pdf -- DU
