[Dovecot] 3 node setup without cluster filesystem

[Kui Zhang]

On Thu, Mar 28, 2013 at 5:43 PM, Daniel Parthey <
daniel.parthey at informatik.tu-chemnitz.de> wrote:

> Michael wrote:
> > short version: Is there any 3 host (two MX and one frontend IMAP) that
> > can use a shared (iSCSI) ext4 volume?
>
> No. iSCSI exports a block device from one host to another single host.
>
>
No, you can export iSCSI to multiple host.


> > Long version:
> > I am running a very complex setup right now with two MX, two
> > proxies(lmtp/imap)/imap-frontends and two backends mounting an
> > ocfs2 volume.
> >
> > I would like to reduce the complexity (and the number of hosts) and
> > get rid of ocfs2. I ask myself if I can use an ext4 iSCSI-LUN using
> > this setup:
> >
> > MX01 -> lmtp:unix:private/dovecot-lmtp -> mail_home: /var/mail
> > MX02 -> lmtp:unix:private/dovecot-lmtp -> mail_home: /var/mail
> > IMAP01 (imap) -> mail_home: /var/mail
>
> You cannot mount an iSCSI device simultaneously from different hosts
> without using any locking/cluster filesystems. Otherwise you would
> risk corrupting your ext4 filesystem.
>
> Use NFSv4, DRBD or any other clustering mechanisms to provide
> high availability while preserving data integrity.
>
> Regards
> Daniel
> --
> https://plus.google.com/103021802792276734820
>


Problem is ext4, It is not a cluster file system, as far as I know. So, it
does not coordinate file locking, across multiple nodes. It would result
corruptions.

You could get it down to 2 nodes, with drbd and any non cluster file
system. Since only one node, that does the I/O. Any file system would work.
I like xfs better than ext4.

mx01 -> lmtp: tcp (vip) / (dovecot imap) -> mail_home
mx02 /

Google for "mysql drbd pacemaker". The configs are similar.


Kui.Z