Live migrating index/control files

[azurit at pobox.sk]

Sorry, accidentaly sent the uncomplete message.

Here is the mentioned script (see some configuration directives at the  
beginning of the script):
https://pastebin.com/ArG8zspi




Citát azurit at pobox.sk:

> Hi,
>
> i think you cannot do this without preventing users to log in. We  
> were doing similar thing few years ago and i wrote a Python script  
> for this purpose - you can use it if you find it usefull (script is  
> copying only control files as indexes are transparently recreated):
>
>
>
>
>
> Citát Eirik Rye <rye at trojka.no>:
>
>> Hello,
>>
>> We are running a director-based dovecot cluster where the user's  
>> maildir and the indexes/control files are, for legacy reasons,  
>> stored on separate NFS-backends, i.e.:
>>
>>  mail_location =  
>> maildir:~/Maildir:CONTROL=/mail/control/%1u/%2u/%u:INDEX=/mail/index/%1u/%2u/%u
>>
>> Both ~/Maildir and /mail/{control,index}/ are separate NFS-mounts,  
>> and we now want to consolidate all files to the user's home  
>> directory instead. The end goal is to stop using NFS altogether.
>>
>> I have devised a four step plan for gradually migrating the  
>> index/control files into the user's maildir, on a per-user basis:
>>
>> 1. Kick the user in an attempt to flush the user's index files:
>>
>>  `doveadm director kick <username>`
>>
>> 2. Rsync the index/control files into the user's maildir:
>>
>>  `rsync -uav /mail/{index,control}/${user:0:1}/${user:0:2}/${user}/  
>> /mail/${user:0:1}/${user:0:2}/${user}/Maildir/;`
>>
>> 3. Update the (redis-based) userdb for the specific user to  
>> override mail_location to use the default CONTROL/INDEX locations:
>>
>>  `{"mail": "maildir:~/Maildir"}`
>>
>> 4. Kick the user one last time so that they reconnect using the new  
>> settings.
>>
>> Unfortunately, after running this for a small batch of users, we  
>> recieved a couple reports that their clients had started to  
>> resynchronize and redownload their mailboxes, which is exactly what  
>> we're trying to avoid. There are no index related error messages  
>> related to the few users that reported these issues.
>>
>> From my understanding, clients become confused when the control  
>> files are changed or lost (`dovecot-uidlist` and  
>> `dovecot-uidvalidity`), so I suspect the kick + rsync + kick  
>> procedure is not robust enough for this.
>>
>> Does anyone have any experience with performing such a migration  
>> without taking systems offline for the duration? Any suggestions to  
>> make this process more transparent for our users, so as to not  
>> induce panic when their mailboxes abruptly appear empty?
>>
>> Best regards,
>> Eirik