[Dovecot] 3 node setup without cluster filesystem
Hi everyone,
short version: Is there any 3 host (two MX and one frontend IMAP) that can use a shared (iSCSI) ext4 volume?
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
Regards Michael
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
On Thu, Mar 28, 2013 at 5:43 PM, Daniel Parthey < daniel.parthey@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
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
On Friday 29 March 2013 01:18:13 Michael wrote:
short version: Is there any 3 host (two MX and one frontend IMAP) that can use a shared (iSCSI) ext4 volume?
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:
You could manage the mailboxes only on one machine with using lmtp over network (http://wiki2.dovecot.org/LMTP):
MX01 -> lmtp:unix:private/dovecot-lmtp -> mail_home: /var/mail MX01 -> lmtp:inet:<ip of imap01>:24 -> IMAP01-> mail_home: /var/mail MX02 -> lmtp:unix:private/dovecot-lmtp -> mail_home: /var/mail MX02 -> lmtp:inet:<ip of imap01>:24 -> IMAP01-> mail_home: /var/mail IMAP01 (imap) -> mail_home: /var/mail
So only one node accesses the mail storage and every filesystem should work.
Bye Malte.
participants (4)
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Daniel Parthey
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Kui Zhang
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Malte Swart
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Michael