[Dovecot] Performance of Maildir vs sdbox/mdbox

[Mark Moseley]

<snip>
>>> * All mail storage presented via NFS over 10Gbps Ethernet (Jumbo Frames)
>>>
>>> * Postfix will feed new email to Dovecot via LMTP
>>>
>>> * Dovecot servers have been split based on their role
>>>
>>>  - Dovecot LDA Servers (running LMTP protocol)
>>>
>>>  - Dovecot POP/IMAP servers (running POP/IMAP protocols)
>>
>>
>> You're going to run into NFS caching troubles with the above split
>> setup. I don't recommend it. You will see error messages about index
>> corruption with it, and with dbox it can cause metadata loss.
>> http://wiki2.dovecot.org/NFS http://wiki2.dovecot.org/Director
>
>
> That might be the one thing (unfortunately) which prevents us from going
> with the dbox format.  I understand the same issue can actually occur on
> Dovecot Maildir as well, but because Maildir works without these index
> files, we were willing to just go with it.  I will raise it again, but there
> has been a lot of push back about introducing a single point of failure,
> even though this is a perceived one.
</snip>

I'm in the middle of working on a Maildir->mdbox migration as well,
and likewise, over NFS (all Netapps but moving to Sun), and likewise
with split LDA and IMAP/POP servers (and both of those served out of
pools). I was hoping doing things like setting "mail_nfs_index = yes"
and "mmap_disable = yes" and "mail_fsync = always/optimized" would
mitigate most of the risks of index corruption, as well as probably
turning indexing off on the LDA side of things--i.e. all the
suggestions at http://wiki2.dovecot.org/NFS. Is that definitely not
the case? Is there anything else (beyond moving to a director-based
architecture) that can mitigate the risk of index corruption? In our
case, incoming IMAP/POP are 'stuck' to servers based on IP persistence
for a given amount of time, but incoming LDA is randomly distributed.