[Dovecot] Migration from v1 to v2 with hashed directory structure

[Steffen Kaiser]

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On Thu, 28 Feb 2013, Ed W wrote:
> On 28/02/2013 13:59, Pavel Dimow wrote:
>> Hi,
>> 
>> I want to upgrade to version 2 but I would like to solve a long
>> standing problem with 'flat' directory structure ie
>>   we have /var/spool/vmail/mydomain.com/user at mydomain.com and I want a
>> new server with version 2 to have
>> hashed directory structure like /var/spool/vmail/mydomain.com/u/s/user
>> I was wondering it f there is some better solution then dir hashing or
>> a way to hash a dir other then first two letters.
>> Also any suggestion how to perform this migration from old to new
>> server with hashing on the fly?
>> 
>
> My thought would be that unless you have millions of users, such a rename 
> process will take only seconds to minutes?  Why not just take the server down 
> for a couple of minutes to do the rename process?
>
> If you wanted to be really clever, you could do it live using symlinks to 
> move the dirs, then update the dovecot config?

Yeah:

for dir in /var/spool/vmail/mydomain.com/*; do
  to="$(script_to_map_name "$dir")"
  if ! test -d "$(dirname "$to")"; then
     # add -m 0555 if needed
     mkdir -p "$(dirname "$to")"
  fi
  # If a new mails arrives or the user access the box
  # there will be an error for a (very) short time
  mv "$dir" "$to"
  ln -s "$to" "$dir"
  # no more errors 
done

Then update the config, reload Dovecot, wait a bit, remove the symlinks.

- -- 
Steffen Kaiser
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