slow IMAP data transfer

Michael Loftis mloftis at
Thu Feb 9 16:21:01 EST 2006

--On February 9, 2006 10:46:29 AM +0000 David Carter <dpc22 at> 

> Cyrus and Postfix both make very heavy use of fsync() to flush data to
> disk before they confirm actions back to the sending system. RAID
> controllers or disk boxes with battery backed writeback cache help lots.

I'll confirm what David and Henrique both posted.  Cyrus, postfix, and 
friends, make a LOT of use of fsync.  This will cause a lot of I/O, esp if 
your RAID doesn't have a write cache.  I'd also suggest only using a 
battery backed write cache.

We see similar behavior on Linux with Cyrus, Postfix, and MailScanner (also 
running SpamAssassin).  If/when we get into a situation where our AX100 or 
CX200 disable their write caches the mailserver usually pretty much pukes 
since it's constantly causing sync's.

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