[Ocfs2-users] Shared Writeable MMAP

[Robert Schetterer]

Am 12.06.2013 20:56, schrieb Joel Becker:
> On Wed, Jun 12, 2013 at 02:27:05PM +0200, Robert Schetterer wrote:
>> Hi @ll i have a question about feature
>> Shared Writeable MMAP and its relation to concurent file use.
>>
>> Background, over years i am hosting dovecot imap servers behind
>> loadbalancers on a drbd master/master setup shared formated storage
>> ocfs2 1.4.3 maildir without problems.
>>
>> the dovecot wiki says
>>
>> http://wiki2.dovecot.org/Director
>>
>> Director can be used by Dovecot's IMAP/POP3/LMTP proxy to keep a
>> temporary user -> mail server mapping. As long as user has simultaneous
>> connections, the user is always redirected to the same server. Each
>> proxy server is running its own director process, and the directors are
>> communicating the state to each others. Directors are mainly useful for
>> setups where all of the mail storage is seen by all servers, such as
>> with NFS or a cluster filesystem
>>
>> so the director service is most installed on the loadbalancers mainly
>> with nfs storage, proved to be a "must have"
>>
>> after online investigation and long lasting reality tests , i guess "or
>> a cluster filesystem " isnt true for ocfs2, cause on drbd it works fine
>> with concurent files use ( i.e mailbox format maildir ) by feature
>> Shared Writeable MMAP.
>>
>> Can sombody confirm this, or teach in easy words how it works ( or not )
>> and why ?
> 
> 	I'm not sure what you are asking.  I *think* you are saying,
> "ocfs2 is not a sufficient cluster filesystem for Dovecot

no my meaning is reverse of that, i am running it fine since years ,
but others believe using a director service on the loadbalancer is a
"must have" avoiding concurent use of shared maildir storage and dovecot
indexes, which is definite true for nfs, but for my understanding its
not needed using drbd/ocfs2 cause of feature  i.e Shared writeable mmap
or additional features.

In using that setup over years without directors, i didnt noticed any
errors nor i could produce one with file tests or with imap clients

, because it
> does not have shared writeable mmap(2)."  If that's what you are saying,
> then you are incorrect.  Shared writeable mmap(2) is a very standard
> feature of ocfs2; we can't be POSIX without it.
> 	I also don't understand how you are configured.  Because it
> sounds like you are using ocfs2+drbd successfully, which conflicts with
> your statement that ocfs2 is not a sufficient cluster filesystem.

sorry ,descriptions of what exact "Shared writeable mmap" is, is hard to
understand for none kernel hackers which are not natural english
speakers, so i asked for clarification

> 
> Joel
> 
>>
>>
>> Best Regards
>> MfG Robert Schetterer
>>
>> -- 
>> [*] sys4 AG
>>
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>>
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>>
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> 



Best Regards
MfG Robert Schetterer

-- 
[*] sys4 AG

http://sys4.de, +49 (89) 30 90 46 64
Franziskanerstraße 15, 81669 München

Sitz der Gesellschaft: München, Amtsgericht München: HRB 199263
Vorstand: Patrick Ben Koetter, Axel von der Ohe, Marc Schiffbauer
Aufsichtsratsvorsitzender: Florian Kirstein