High-availability LH* schemes with mirroring

Mirroring is a popular technique for enhancing file availability. The authors incorporate this technique into the LH* algorithms for scalable distributed linear hash files. Several schemes for mirroring LH* files are presented in this paper. The schemes increase the availability of LH* files in the presence of node failures. Every record remains accessible in the presence of a single node failure, and usually in the presence of multiple-node failures. The price is, as usual, twice as much storage for data, and an increase in the number of messages. The different schemes are characterized by different trade-offs, and they accommodate diverse application requirements. The additional messaging cost per insert is about the same for all the schemes, and is roughly only one message. The cost of a bucket recovery may in contrast vary greatly, from one message for one type of scheme, to a few for another, and many for yet another.