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

Thank you for reply,

BTW, other webserver has almost the same bonnie results (10283ms and 5884ms) on ext3 partition with 45GB of data (1.5 millions of files)?!

Hardware and RAID5(also hardware) are the same: HP Proliant DL380 G4 with SmartArray 6i controller (as I see it comes with 128MB BBWC enabler but not kit).

I did not tried to mount fs with barriers disabled. Does it have any crititcal risks?

Bonnie tests was performed in the morning when we have a mininmal user load.

But why the same server with the same RAID(4 disks) but with FreeBSD+UFS was much better? I guess problem is in ext3 then?

With regards, Andrey.

23.09.2011 11:31, Janne Pikkarainen пишет:

On 09/23/2011 08:51 AM, 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?

With regards, Andrey


(replying off-list, so the ext3 developers will not start a flamewar)

In my opinion ext3 is a terrible file system for your kind of workload,
especially if you have lots of concurrent clients accessing their
mailboxes. Even though ext3 has evolved over the years and has gained
features such as directory indexes, it still is not good for tens of
million of frequently changing small files with lots of concurrency.
Been there, done that, not gonna do it again. I administer servers with
50 000 - 100 000 user accounts, with couple of thousands active IMAP

Personally I switched from ext3 to ReiserFS many years ago and happily
used it between 2004-2008, then after things went downhill from ReiserFS
development point of view, I switched to XFS during a server hardware
refresh. ReiserFS was excellent, but it really started to slow down if
file system was more than 85% full and it also got fragmented over time.

XFS has been rock-solid and fast since 2008 for me, but it has an
achilles heel of its own: if I need to remove lots of files from a huge
directory tree, the delete performance is quite sucky compared to other
file systems. This has been improved in the later kernel versions with
the new delaylog parameter, but how much, I've not yet tested.

All this said, the performance of ext3 should not be THAT bad you are
describing. Is the bonnie result done while the server is idle or while
it has mail clients accessing it all the time? If you have hardware
RAID, is there a battery-backed up write cache and are you sure it's
enabled? Also, have you tried to mount your file system with barriers
disabled? What kind of server setup you have?

Something is very wrong.

Best regards,

Janne Pikkarainen

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