Migrating from UW-Imap to Cyrus

Aleksandar Milivojevic alex at milivojevic.org
Tue Feb 14 10:24:12 EST 2006

Quoting Michael Menge <Michael.Menge at zdv.uni-tuebingen.de>:

> Hi,
> I was testig imapsync to migrate from UW-Imap to Cyrus.
> It seems to have very usefull options for renaming Folders. But i 
> only got 100k/sec. Even running 5 processes of imapsync i got little 
> over 100kB/s in the summ. Imapsync  seemed to consume much cputime 
> and was faster by handling large Messages.
> Runing 2 processes of imapsync on differnt server, with the same 
> destination and target got me a speed of over 200k, but to convert 
> 40000 user with about 15-50MB each i would at least need 5-10MB/s
> Is ther a way to make imapsync run faster ore are there faster Programs?

The problem with programs such as imapsync (when used for large 
migrations) is that they use IMAP protocol which imposes considerable 
overhead.  It will always be much slower then copying files directly.

If you don't need to maintain flags during your move 
(read/answered/deleted), you might be better off writing couple of 
scripts to do the job.  The first script would pre-create all mailboxes 
and folders, the second script would split Berkely style mailboxes into 
one-file-per-email and save them into cyrus look-alike directory 
structure.  Then you would simply run reconstruct on those mailboxes to 
recreate cyrus databases.  This is by far the fastest way to migrate, 
but as I said, it might not be option for you (users are sure to 
complain all their email is marked as unread, they lost information if 
they replied to the email, all mail marked as deleted will also appear 
as new).

Since wu-imapd stores those flags in email headers, you might try 
patching reconstruct to parse wu-imapd headers and use information 
found in them to set correct flags.  Make sure you restore old 
unpatched reconstruct once migration is done!  However, I never heard 
of anybody doing something like that.

Back to imapsync.  Imapsync wasn't really written with migration in 
mind.  It was more of a tool to keep two IMAP mailboxes in sync.  While 
ago I patched it to add couple of "speed" options and make it more 
usefull for migration tasks.  I've sent the patch to the author, he 
asked me if I could do some changes and resubmit, but unfortunately I 
never found time to do it.  Don't know if he included any of those into 
later releases.  And it was pain in the ass to communicate with him 
since back then he was using some braindead anti-spam software (some 
variation of those chalange-response systems).  If you want, I can 
email you privately patched version with those extra options.  However, 
it probably isn't going to give you the speed you want (but you might 
try and see if it will still be usefull).

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