[ILUG] far flung redundancy

[greg wm]

we want redundant mailservice, colocated with data mirrors in more than 
one country, connected via different ISPs, without using a usa or uk 
company.  outsourcing would be sensible, any recommendations?

the other possibility is install it ourselves.  is there such software 
in the open source world?

i'm envisioning multiple servers, robust enough to handle communications 
outages where some users manage to connect to one server and other users 
manage to connect to another server.  so each server should be able to 
directly and simultaneously serve IMAP clients, keeping the filesystems 
in sync on the fly, or as soon as possible.  it doesn't seem 
particularly complicated in theory, just that it would want to be 
implemented on the filesystem level.  using rsync wouldn't suffice, 
rsync is too much latency, too much overhead, and not multidirectional. 
  unison has similar and other shortcomings.

it seems entirely simple right upto the part where you try to define 
what constitutes a simultaneous update of a single file, and what to do 
when it happens.  perhaps a .eunifs parameter file might tweak how 
things are handled within that portion of the fs.  for example, how long 
to wait before bothering to pass locally updated data on to the other 
servers, or, what user to notify about simultaneous updates and how to 
reach her.

things slightly OT that arguably might make sense to do at the same 
time:  keep old copies of files for possible user retrieval.  maintain 
an md5 index of files, and use it to avoid storing or sending data when 
an identical file exists (ala Backup-PC).

so but anyway, does it exist already?  and if not, any suggestion of who 
  might be up for implementing, and how to find them?

tia,
greg wm
IT Coordinator
NonviolentPeaceforce.org