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.