ext3 with maildir++ = huge disk latency and high load

Andrey basketboy at bk.ru
Sat Sep 24 17:46:49 UTC 2011

Sure, indexing is on by default on Debian ext3. I think I'll try to test 
some cases an run bonnie++ on freesh HP server with the same configuration.

Also I have maildir with more than 10000 messages an don't have 
timesouts and access problesm via IMAP to it, that's strange. Sometimes 
I notice that copying message to Sent folder can wait a little but it's 
a seldom issue but can corellate with it, I agree. Also I see in Exim 
logs that DT (delivery time) is equal to more than 2 seconds although 
user's maildir is almost empty, so I intend to that it is a primary 
problem of whole ext3 system or RAID5 hardware.

23.09.2011 21:19, Bob пишет:
> On 09/22/2011 11:51 PM, Andrey wrote:
>> Hello,
>> I have a production mail server with maildir++ structure and about
>> 250GB (~10 millions) of files on the ext3 partition on RAID5. It's
>> mounted with noatime option. These mail server is responsible to local
>> delivery and storing mail messages.
>> System has Debian Squeeze installed and Exim as MDA + Dovecot as
>> IMAP+POP3 server.
>> Bonnie results are terrible. Sequential output for Block and Rewrite
>> are 10722ms and 9232ms. So if there is a 1000 messages in the mail
>> queue load is extremely high, delivery time is very big and server can
>> hang. I did not see such problems with UFS on FreeBSD server.
>> As I understand ext3 file system is really bad for such configurations
>> with Maildir++ (many smaill files)? Is there a way to decrease disk
>> latency on ext3 or speed up it?
> My guess is that your problem is many files in one directory not
> necessarily
> having many files on the whole file system. In my experience large
> directories
> eat ext3's lunch. The introduction of indexing did help but it still
> fell behind
> on performance when compared to some other file systems. You may want
> to make sure your file system has indexing turned on but with the
> vintage of
> your Debian I would assume it is on by default.
> I ran into this problem many years ago (before indexing was an ext3
> option). It
> was even worse as the Maildir storage was being accessed over NFS. Ended
> up eventually biting the bullet and moving to WAFL (NetApp).
> My guess is that users trying to access these large directories via IMAP
> and POP
> are also facing large delays and possibly even time outs.
> Steven
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