[Dovecot] Live Mirror dovecot / OS X 10.6.4 (Timo Sirainen)

[Thomas von Eyben]

On Wed, Aug 25, 2010 at 4:27 PM, Eric Boltz (MMI/UPC)
<eboltz at marathonmonitors.com> wrote:
>
> On Aug 25, 2010, at 10:15 AM, Timo Sirainen wrote:
>>
>> But if secondary server allowed changes, this is the difficult step to
>> do correctly. For example lets say in first server:
>>
>> 1. It rsyncs user foo
>> 2. User foo changes message A flag to \Seen
>> 3. User foo deletes message B
>> 4. User foo saves a new message C
>> 5. The server crashes
>> 6. Secondary server goes up, but 2-4 changes weren't resynced yet
>> 7. User foo logs in and changes message D's flag to \Seen
>> 8. Primary server goes back up
>> 9. You rsync .. how? If you make primary server look exactly like
>> secondary server, you message C gets lost. If you copy new files, now
>> message A and message D gets duplicated, because their filename changed
>> due to the flag change. Also message B becomes undeleted.
>>
>> Of course assuming this happens rarely enough, those aren't a huge
>> problem, but the server move isn't always transparent to users and
>> you'll get errors in Dovecot's logs.
>
> First off, thanks.
> It will happen rarely (2-3x/year most likely base on prior power outages) and if a couple users get a duplicate message or unread when read issue they can file a complaint :)
> The transfer wouldn't be transparent - I would force them to webmail on the backup (maybe even force POP3?).
>
> Now to figure out where the virtual user data is...sigh
>
Would the "users" be the users in the Open Directory?

If that's the case then you could probably "just" make the "backup"
server an Open Directory Replica thus it would allways contain a (read
only) copy of the user database…

PS.: I am also thinking about how to make a "hot standby" OS X 10.6.x
Server mail server ;-)

- TvE