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

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:

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
having many files on the whole file system. In my experience large
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.


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