[Dovecot] Questions regarding dbox migration

[Timo Sirainen]

On Oct 14, 2009, at 7:03 AM, Mikkel wrote:

> It has been my wish to move to dbox for a long time hoping to reduce  
> the number of writes which is really killing us.
>
> Now I wonder what may be the best way of doing so. I'm considering  
> some sort of intermediate migration where the existing Maildir users  
> are changed to single-dbox and then later upgraded to 2.0 and  
> changed to multi-dbox when it becomes stable.
> But is this a reasonable task to perform on a production system or  
> at all? The alternative is to wait for 2.0 to become completely  
> stable and then go all the way at once.

I'd wait for v2.0 if possible. v1.2's dbox has a couple of problems:

1. antispam plugin doesn't work
2. copying messages can't currently be done by hard linking, so  
copying uses more disk I/O (this could be fixed somewhat easily  
though, just haven't had time)
3. flags are backed up to individual dbox files "once in a while", but  
probably practically pretty often so that also increases disk I/O usage

v2.0 already solved 3 for single+multi-dbox, 2 for multi-dbox and I'm  
not sure about 1.

> Now the big question is whether multi-dbox and single-dbox are  
> compatible formats.

Kind of, but not practically.

> If a Maildir->dbox migration is made on a system running dovecot v.  
> 1.1, would it then be trivial later changing to multi-dbox after  
> upgrading to 2.0 or is a completely new migration then needed?
> Would this scenario be much different if the system is upgraded to  
> version 1.2 before the change to single-dbox?

Migrating from single-dbox to multi-dbox isn't any easier than maildir  
-> multi-dbox.

I'm trying to get v2.0.0 out pretty quickly though. v2.0.beta1 should  
hopefully be out in less than a month. The main problem with it is  
actually how to make it enough backwards compatible that everyone  
won't start hating me.