[Dovecot] distributed mdbox

[Jim Lawson]

On 3/23/12 3:13 AM, Stan Hoeppner wrote:

>> Speaking as an admin who has run Dovecot on top of GFS both with and
>> without the director, I would never go back to a cluster without the
>> director.  The cluster performs *so* much better when glocks can be
>> cached on a single node, and this can't happen if a single user has IMAP
>> processes on separate nodes.
>>
>> No, you don't strictly need the director if you have GFS, but if you can
>> manage it, you'll be a lot happier.
> Did/do you see the Director/glock benefit with both maildir and mdbox
> Jim?  Do you see any noteworthy performance differences between the two
> formats on GFS, with and without Director?  BTW, are you hitting FC or
> iSCSI LUNs?
>

Actually, we're all mbox.  This primarily has to do with how users do
self-service mail recovery from backup: one folder = one file.

I'd like to move to mdbox, but it would mean the recovery scripts will
need to understand which files are associated with which folders, as
well as restoring the associated index files.  That's a to-do.

We're using fibrechannel (IBM v7000) storage, but I would expect to see
the same thing with iSCSI.  It's mostly about different nodes contending
over locks on the same files (although I'm sure cache locality helps a
great deal, too.)  If you end up with imap processes for the same folder
on different nodes, or mail delivery happening on one node and imap on
the other, you will feel the lag in your IMAP client.  "Oh, my INBOX has
been unresponsive for 10 seconds, I must be getting a lot of mail right
now!"  That's an exaggeration, but not by much.

Jim