On 1/27/2012 2:57 PM, Timo Sirainen wrote: > On 27.1.2012, at 20.11, Simone Caruso wrote: > >>> I have a customer with 3 different geographic locations. >>> >>> Every locations have a mail server for the same domain (example.com). >>> >>> If us...@example.com receive mail form external this mail going on >>> every locations server. >>> >>> I've a problem now, is it possible to syncronize the state (mail flag) >>> of user1 imap folder mails on every mail locations server? >> >> Syncronize your storage with DRBD, (or async replica like rsync) and use >> dovecot >> director for connection persistence. > > > There are a couple of problems with DRBD and most (all?) other filesystem > based solutions when doing multi-master replication across wide geographic > locations: > > 1. Multi-master requires synchronous replication -> latency may be very high > -> performance probably is bad enough that the system is unusable. > > 2. Network outages are still common -> you can't handle split brain > situations in filesystem level without either a) loss of availability > (everyone's email down) or b) data loss/corruption (what do you do when > multiple sites have modified the same file?) > > With dsync-based replication it's possible to avoid both of these problems, > because application-level replication can intelligently handle situations > where asynchronous replication results in data conflicts. (This kind of > conflict resolution is also what I hope to do with some nosql database in > future when Dovecot supports them.) I've been working on dsync-based > easy-to-use replication recently, and it's almost in a condition where I'm > going to start using it myself (maybe this weekend).
Can you provide a basic diagram/high level description of how this dsync replication would be configured to work over a 2 node wide area network? Are we looking at something like period scripts, something more automatic, a replication daemon? -- Stan
