[Dovecot] Migration questions...

[Richard Hobbs]

Hello,

Apologies for replying to my own email so soon, but I've had other
thoughts as well...

Our server is going to have 4 hard disks. These can be configured into 2
RAID 1 (mirror) arrays, a single RAID 5 array, or a single RAID 0+1 array.

Previously, we thought that two RAID 1 arrays would be best because the
inboxes can sit on one set of disks, and the IMAP folders on another.
This is so both types of user don't annoy each other. However, with no
knowledge of how the highest performing mailbox format works with
dovecot, perhaps this isn't the best option.

Basically, i suppose i'm asking, with the highest performing mailbox
option, is dovecot going to run faster with 2 individual arrays each
made from 2 disks, or a single 4-disk array (in which case we'd go RAID
0+1)?

Also... would it be useful to turn off "atime" when we mount the
volume(s) or does dovecot rely on this?

Thanks again, people... :-)

Richard.


Richard Hobbs wrote:
> Hi All,
> 
> We are soon to migrate our mail server from one piece of hardware to
> another and we would like to take this opportunity to optimize things.
> As a result, we would like to replace "uw-imapd" and "qpopper" with
> "dovecot". The version we will be installing is 1.1.13-2, as this is
> what is available through the latest Debian stable backports. We will
> also be using exim to deliver mail (through dovecot's deliver mechanism,
> of course).
> 
> So... We are currently using the mbox format with uw-imapd, and would
> like to migrate to the fastest solution possible with dovecot on the new
> hardware. My understanding is that "multi-dbox" is not an option in this
> version anyway, maildir is OK, but not great, and "single-dbox" is
> therefore going to be the highest performing solution. Is single-dbox
> the fastest way to go, considering we're going to be using email in the
> following ways:
> 
>  - IMAP connections with all email in the Inbox (Gmail-style).
>  - IMAP connections with email split into many IMAP folders.
>  - POP3 connections with no email left on the server.
>  - POP3 connections with *all* email left on the server.
> 
> All connections check for new mail every 5 minutes (on average) and
> there are 50-60 users). Also, we are not able to change user behaviour
> in this instance, unfortunately.
> 
> Can anyone see any problems with the above proposal? Hopefully not...
> 
> One problem that may arise is the fact that when we migrate, all msg
> UIDs will be lost. If i'm not mistaken, this means that all emails will
> be treated by the mail client as brand new, and if through IMAP, will
> all go bold, and if through POP3, will all be downloaded again (if still
> on the server) and therefore duplicated in the mail client. If this is
> the case, is there anything we can do to stop this happening? Does the
> "Convert" plugin does this job well?
> 
> Finally, I have a rough draft of our migration plan - is there anything
> horribly wrong in it that's going to cause lots of problems, that anyone
> can spot by any chance?
> 
> 1. Install Debian with exim, mysqld (for Horde/IMP) and mailman.
> 
> 2. Run an online update.
> 
> 3. Rsync homedirs and inboxes onto new server, ready for initial exim
> configuration.
> 
> 4. Configure exim as per existing mail server and test that mailing
> lists and normal email works.
>    You should now have the existing mail delivery solution on the brand
> new hardware.
> 
> 5. Once mail delivery is sorted, add "deb
> http://www.backports.org/debian lenny-backports main contrib non-free"
> into "/etc/apt/sources.list" and run "aptitude update && aptitude
> install debian-backports-keyring && aptitude update".
> 
> 6. Install dovecot (at the time of writing, this was version 1.1.13-2)
> and configure to use existing mbox files (inboxes in /var/spool/mail/
> and IMAP folders in /home/user/mail/)
> 
> 7. Setup exim to use dovecot's "deliver" mechanism for interacting with
> the inboxes (which are still in mbox format).
> 
> 8. Configure the "convert" plugin to begin converting the mail to dbox
> format.
> 
> 9. Run something manually (if possible) to convert mailboxes before
> people connect, so the task is already done by the time the outage is over.
> 
> 10. Give staff access to new speedy mail server!
> 
> Thanks in advance, people - any help is greatly appreciated! :-)
> 
> Richard.
> 

-- 
Richard Hobbs (IT Specialist)
Toshiba Research Europe Ltd. - Cambridge Research Laboratory
Email: richard.hobbs at crl.toshiba.co.uk
Web: http://www.toshiba-europe.com/research/
Tel: +44 1223 436999        Mobile: +44 7811 803377
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