README.md

@@ -1,32 +1,46 @@
-# Machi
+# Machi: a robust & reliable, distributed, highly available, large file store
 
   [Travis-CI](http://travis-ci.org/basho/machi) :: ![Travis-CI](https://secure.travis-ci.org/basho/machi.png)
 
-Our goal is a robust & reliable, distributed, highly available(*),
-large file store based upon write-once registers, append-only files,
-Chain Replication, and client-server style architecture.  All members
-of the cluster store all of the files.  Distributed load
-balancing/sharding of files is __outside__ of the scope of this
-system.  However, it is a high priority that this system be able to
-integrate easily into systems that do provide distributed load
-balancing, e.g., Riak Core.  Although strong consistency is a major
-feature of Chain Replication, first use cases will focus mainly on
-eventual consistency features --- strong consistency design will be
-discussed in a separate design document (read more below).
+Our goal is a robust & reliable, distributed, highly available, large
+file store.  Such stores already exist, both in the open source world
+and in the commercial world.  Why reinvent the wheel?  We believe
+there are three reasons, ordered by decreasing rarity.
 
-The ability for Machi to maintain strong consistency will make it
-attractive as a toolkit for building things like CORFU and Tango as
-well as better-known open source software such as Kafka's file
-replication.  (See the bibliography of the [Machi high level design
-doc](./doc/high-level-machi.pdf) for further references.)
+1. We want end-to-end checksums for all file data, from the initial
+   file writer to every file reader, anywhere, all the time.
+2. We need flexibility to trade consistency for availability:
+   e.g. weak consistency in exchange for being available in cases
+   of partial system failure.
+3. We want to manage file replicas in a way that's provably correct
+   and also easy to test.
 
-    (*) When operating in strong consistency mode (supporting
-    sequential or linearizable semantics), the availability of the
-    system is restricted to quorum majority availability.  When in
-    eventual consistency mode, service can be provided by any
-    available server.
+Of all the file stores in the open source & commercial worlds, only
+criteria #3 is a viable option.  Or so we hope.  Or we just don't
+care, and if data gets lost or corrupted, then ... so be it.
 
-## Status: mid-October 2015: work is underway
+If we have app use cases where availability is more important than
+consistency, then systems that meet criteria #2 are also rare.
+Most file stores provide only strong consistency and therefore
+have unavoidable, unavailable behavior when parts of the system
+fail.
+What if we want a file store that is always available to write new
+file data and attempts best-effort file reads?
+
+If we really do care about data loss and/or data corruption, then we
+really want both #3 and #1.  Unfortunately, systems that meet criteria
+#1 are *very*
+rare.  Why?  This is 2015.  We have decades of research that shows
+that computer hardware can (and
+indeed does) corrupt data at nearly every level of the modern
+client/server application stack.  Systems with end-to-end data
+corruption detection should be ubiquitous today.  Alas, they are not.
+Machi is an effort to change the deplorable state of the world, one
+Erlang function at a time.
+
+## Status: mid-December 2015: work is underway
+
+TODO: status update here.
 
 * The chain manager is ready for both eventual consistency use ("available
   mode") and strong consistency use ("consistent mode").  Both modes use a new
@@ -53,9 +67,18 @@ If you'd like to work on a protocol such as Thrift, UBF,
 msgpack over UDP, or some other protocol, let us know by
 [opening an issue to discuss it](./issues/new).
 
+## Where to learn more about Machi
+
 The two major design documents for Machi are now mostly stable.
 Please see the [doc](./doc) directory's [README](./doc) for details.
 
+Scott recently (November 2015) gave a presentation at the
+[RICON 2015 conference](http://ricon.io) about one of the techniques
+used by Machi; "Managing Chain Replication Metadata with
+Humming Consensus" is available online now.
+* [slides (PDF format)](http://ricon.io/speakers/slides/Scott_Fritchie_Ricon_2015.pdf)
+* [video](https://www.youtube.com/watch?v=yR5kHL1bu1Q)
+
 ## Contributing to Machi: source code, documentation, etc.
 
 Basho Technologies, Inc. as committed to licensing all work for Machi