[Dovecot] HA Dovecot Config?
rick at havokmon.com
Wed Oct 21 23:35:07 EEST 2009
Quoting "Eric Rostetter" <rostetter at mail.utexas.edu>:
> Quoting Rick Romero <rick at havokmon.com>:
>> They claim to be real-time, and with kernel hooks into
>> reads/writes, it seems promising to run on top of the OS..
> Yes, but that doesn't mean it will work in the cluster environment...
> It also says things like:
>> There are different types of file locks. In addition to these differences,
>> each OS has its own set of rules regarding file locks as well. FRP's
>> replication of locked files will vary in relation to the way the OS treats
>> these types. However, one rule is consistent throughout all operating
>> systems in that exclusive file locks will prevent FRP from replicating data.
> See that last line there??? Want to bet something in the mail setup
> (MTA, dovecot, system jobs like backup, etc) put an exclusive lock on
> files from time to time?
> Again, a fine backup system, and depending on your needs it might be
> okay for a failover setup, but not for an active-active setup. For
> that you need a lock manager, which they promise "in the future" but
> don't deliver yet...
I thought the entire reason (ok not the _entire_ reason but..) for
Maildir was to avoid locks and allow easy concurrent access to a
mailbox through many different applications.
From DJB's page: http://cr.yp.to/proto/maildir.html
Why should I use maildir?
Two words: no locks
So while I do agree that file locking is a possible problem in an
active/active setup with FRP, I think it's possible - as long as the
admin is aware of the risks. So for backup purposes, to avoid locks
for example, use ZFS snapshots.
I'm not even a user of FRP at this point, but it's something that
intrigues me for active/active because of it's OS independence. I
want ZFS. I really enjoy ZFS. I already have active/passive with zfs
sends, I want to step it up :)
Yes, there are definitely things to be aware of. I'm not sure if this
is the place to hash it out, but I think that while it's not a cheap
solution it may fit MY environment - and possibly others who use
I guess everyone is as cheap as I am and hasn't set it up yet :)
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