[Dovecot] performance of maildir on ocfs2

[luben karavelov]

On 29.04.2010 21:02, Timo Sirainen wrote:
> On Mon, 2010-04-26 at 15:51 +0300, karavelov wrote:
>
>    
>> 3. My understanding is that OCFS2 uses a global lock for move/rename.
>> As you know, Maildir format uses a lot of such operations. I think
>> that
>> dbox format (dovecot native) will be better choice, because there are
>> no file moves/renames. I am planning migration to dbox now. If I have
>> to start the service now, I would choose dbox for mail storage.
>>      
> Wonder what the performance difference is then between v2.0's
> single-dbox and multi-dbox? I'd guess mdbox is faster.
>
>    

Here are some benchmarks that were done with imaptest.
The used commands are
imaptest host=rhp2 mbox=dovecot.mbox user=test at example.com pass="test" 
seed=123 secs=10
imaptest host=rhp2 mbox=dovecot.mbox user=test at example.com pass="test" 
seed=123 secs=10 logout=0

The volume is an iscsi export (4 SATA disks in a stripe) mounted on a
imap test server (no other processes are running). On OCFS2 setup, the
filesystem is mounted also on another node (2 node test cluster). The
other node was also idle.

Here are my results:

         Logi List Stat Sele Fetc Fet2 Stor Dele Expu Appe Logo
         100%  50%  50% 100% 100% 100%  50% 100% 100% 100% 100%
                                   30%                  5%
nologout  10  139  130   10  248  350   87  196  248  248       XFS     
maildir
logout   227  121  127  227  216  323   60  170  216  221  454  XFS     
maildir
nologout  10  733  713   10 1438 2094  467 1161 1438 1438       OCFS2   
maildir
logout   584  300  282  584  547  780  170  428  547  580 1168  OCFS2   
maildir
nologout  10  930  892   10 1825 2614  527 1489 1825 1825       OCFS2   dbox
logout   570  290  298  569  564  838  226  452  564  568 1140  OCFS2   dbox


DISCLAIMER: Dovecot server is tuned for best performance with OCFS2 as 
far as
I can because my current production setup is OCFS2 based. XFS is 
included for
comparison without much of tuning. Mount options are:

XFS:   noatime,nodiratime,logbufs=8,logbsize=131072
OCFS2: noatime,data=writeback,commit=30

I have tested also NFS4 but the results were disappointing so I abandoned
further tests because no tuning could make a x10 difference.

My expectation is that pushing dbox in production will have even more gains
than my tests show because it will lower internal OCFS2 locking on move and
rename.

My tests and benchmarks were done using v1.2.11. May be I should make some
benchmarks for mdbox also using dovecot v2. My understanding is that dbox
is forward compatible with mdbox and there will be no need to convert
mailboxes from dbox to mdbox. Is it that ot there will be another pain in
migrationg mailboxes from one format in another?

Best regards
luben