http://gatekeeper.dec.com/pub/DEC/SRC/research-reports/abstracts/src-rr-111.html
Echo is an ambitious distributed file system. It was designed around a
truly global name space. It uses a coherent caching algorithm. It is
fault tolerant. And it is real--it was the primary file system for a
large group of researchers. Its novel aspects include an extensible
"junction" mechanism for global naming; extensive write-behind with
ordering semantics that allow applications to maintain invariants
without resorting to synchronous writes; and fault tolerance mechanisms
that are highly configurable and that tolerate network partitions. It
was designed with the intention that its performance could be as good as
a local file system, while supporting large numbers of clients per
server. Its reliability was designed to be higher than other distributed
file systems, and higher than centralized systems. It was designed to
work well in arbitrarily large networks.