TOFF-2 is a high-performance fault-tolerant file service featuring in a new
Symmetric Primary Backup (SPB) replication model. This model lets all repl
icated servers in a service share the load of a traditional primary server,
and minimizes the communication overhead between servers. TOFF-2 is also t
otally transparent to the client machines, and any host with an NFS client
implementation can use the fault-tolerant service provided by TOFF-2 withou
t any modification. The clients do not have to know anything about replicat
ion and server failures, since the TOFF-2 service cluster looks exactly lik
e a single server over the network. The concept and design of TOFF-2 is int
roduced in this article, and statistics taken from tests on a prototype imp
lementation show promising results. (C) 2000 Elsevier Science Inc. All righ
ts reserved.