Re: DB mail

[Jean-Paul Blaquiere <jeanpaul@blaquiere.id.au>]

> > Is anyone using DB mail for IMAP store?   How reliable is it?
> > 
>
a discussion came up on another mailing list I am on, not so long ago,
comparing IMAP servers.  It ended up in IMAP daemon and filesystem
performance discussion.

to quote a friend of mine who may or may not admin at a not insignificant
ISP in Australia.

********************************************************************************
Correctly configured Dovecot using Maildir++ on properly tuned
reiserfs is the highest performing and most reliable IMAP4 server
I'm aware of.  Using the recent 1.0rc's of course :-)

There are only two options that have worked for my email given the
size of my folders recently (I don't file things, I just have them
in one big folder and sort/search as required):

- Exchange Server (2003) with Entorage using webdav or Outlook 2003
  (cached mode, using MAPI), but note the IMAP performance is
  pretty shocking (web acces, webdav and MAPI all work very well).

- Dovecot/Maildir++/reiserfs with Entorage (using IMAP, set to
  save full messages on client), using Postfix for delivery.

I've also seen that Dovecot/Maildir++/WAFL works quite well for
large  installs, but WAFL isn't an option for smaller
installations :-)

********************************************************************************
The filesystem summary, or why we prefer reiserfs:

To give an opinion from someone who has used the various file systems
in the real world:

Having run a rather busy (200Mbps+ sustained) mirror server with 4TB of
data on some arrays which had a tendency to die frequently and a SCSI
card which liked to lock up, I have only very good things to say about
reiserfs 3.x.

JFS and XFS were a nightmare.  Very bad failure modes.  Even when
they could be recovered, there was lots of corruption after failures,
and ongoing complaints for a long time due to hard to detect corruption
(I ended up having to write programs to 'validate' the contents of
the mirror and nuke files which were all-zeros or failed to validate
based on their extension).  Performance also was pretty poor.

I've also run another 4TB array on a NetFlow server which had some
catastrophic events[1] which reiserfs 3.x recovered from perfectly.

ext3?  With or without directory indexes?

with: performance sucks in many cases.  too much head movement and
duplication.

without: performance sucks in other cases.  linear directory searches
really suck.

If I'm installing a Linux box today, the 3 main options I look at are:

1.  ext2.  Yes, that's right, 2.  Limited features but very stable,
    and you can even undelete :-)

2.  reiserfs 3.x.  Good tools, works well.

3.  NFS -> NetApp(WAFL).  Although if there's a really high NFS load
    and a lot of locking going on, you may need to look at the patches
    on linux-nfs.org

[1] Catastrophic in the context of the server or its disk array,
    not in terms of impact, since of course there's a second server
    with a second NetFlow implementation for validation purposes
    and to cover failures or the primary server :-)





./jp
-- 
Jean-Paul Blaquiere
 jeanpaul@blaquiere.id.au
  http://www.blaquiere.id.au
   http://japester.ucc.asn.au/