Corruption & migration

[Daniel Miller]

I have an existing server using mdbox & sis.  There is a quantity of 
corruption - I have no idea where it came in.  I'd had a previous 
rebuild some years ago and I thought I had a clean datastore.  By 
"corruption" I mean missing attachments and either missing or mixed-up 
emails.

I've setup a new server on a virtual machine.  Instead of copying the 
old configs I hand-adjusted individual settings using the current 
distribution example.  The new server is running...but empty.

So now my intent is to migrate the mail to the new machine.  A few items 
to note:
1.  The existing mail server is the virtual host.  The mails are stored 
locally, in mdbox format, with sis enabled.  And possibly zlib.
2.  The new server, via VirtualBox, is presently configured for 
Maildir.  I may change to sdbox - I'm now a little reserved about mdbox.
3.  Instead of storing the mails within the virtual machine, I'm using 
the host's drive.  This is via an exported NFS4 folder from the host, 
mounted on the guest, using the options: 
"auto,noatime,hard,intr,async,nordirplus".
4.  My intent is to have the new virtual server become the primary mail 
server.  The mail store will continue to be accessed by NFS4. No other 
servers or processes (besides backup) should access the mail store.

So...my question is what is the best method for the migration?

Reading the docs on Dovecot replication I'm still very unsure of how to 
implement it - particularly the "master-master" or "master-client" 
relationships.  The docs are not 100% clear on which server gets which 
options.  I can guess...which I'd really rather not do.  But it seems to 
me getting one-way replication working would be the most "elegant" 
solution here.

Manual dsync is also an option - but again I'm not on which machine I 
should execute which options.

Imapsync is a possibility and the syntax is clear - but very slow in 
execution for 100k mails.

Any suggestions or pointers would be welcome.

-- 
Daniel