[Dovecot] 3 node setup without cluster filesystem

[Daniel Parthey]

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.

> 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
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