Upgrade and Migration

[Ben Carter]

Carson Gaspar wrote:
> Ben Carter wrote:
>> Carson Gaspar wrote:
>>> Ben Carter wrote:
>>>
>>> You have to do the _exact_ same thing with imapsync, unless you want 
>>> to lose email.
>>
>> As has already been pointed out, you are incorrect.  The order is:
>>
>> [Pre-create inboxes with large quotas on new server]
>>
>> 1. Shut off mail delivery to old server
>> 2. Shut off imapd on old server.
>> 3. Bring up new server with imapd running
>> 4. Start mail delivery to new server.
>> 5. Start imapd on old server with a new IP address or bound to a 
>> nonstandard port so MUAs will not get to it.
>> 6. Migrate data using imapsync.
>>
>> And your service can be down literally for only a few minutes if you 
>> plan correctly.
> 
> You have chosen to have users see missing data. You have made a tradeoff 

You can't see missing data ;)

> between correctness and length of downtime by bringing up your new 
> server in a client visible way before you sync your data. I (foolishly, 
> it seems) assumed that you wouldn't want your users to log in to empty 
> mailboxes, and would leave your new server non-user-visible until your 
> sync completed.
> 

Yes, that's the trade-off, obviously.  We forewarned our users a week
or 2 ahead of time though, and let's face it: a lot of retained e-mail
just spins around out there, never to be accessed again.  This is
something done on the weekend and/or at night too, remember.  Also, in
addition to being forewarned, each user got a start-of-migration
message and an end-of-migration message so they knew exactly what was
happening and they knew when their migration was complete.

So, migrating like this, the users can send and receive mail with
almost no interruption, and ours seemed to be quite happy with this.
We didn't hear a peep, and we have a lot of users.  I think that it's
much more important to them to be able to send and receive e-mail
without interruption than to have their old mail present immediately. 
  And, their old mail shows up just as it was in a relatively short
period of time.

Ben

-- 
Ben Carter
University of Pittsburgh/CSSD
bhc at pitt.edu
412-624-6470