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Date: Sun, 11 May 2008 09:47:00 +0200
From: Kris Kennaway <kris@FreeBSD.org>
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To: Svein Skogen <svein-listmail@d80.iso100.no>
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Cc: freebsd-bugs@FreeBSD.org, freebsd-current <freebsd-current@freebsd.org>,
	pjd@FreeBSD.org
Subject: Re: Question regarding mmap on ZFS, or possibly Dovecot
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Svein Skogen wrote:
> I still get massive file corruption when allowing Dovecot to run win 
> mmap enabled on ZFS/FreeBSD RELENG_7 (as of one week ago), and I have 
> seen symptoms of corruption with Samba and mmap on ZFS (although I 
> cannot say with certainty that those samba files were corrupted in the 
> FreeBSD end, they may have been mangled by my less-than-trustworthy 
> windows).
> 
> For dovecot+mmap+zfs I get a googlefull of results, same with 
> samba+mmap+zfs.
> 
> The question remains the same, however. Is this a problem with 
> samba/dovecot using mmap incorrectly, a problem with ZFS as such, or a 
> problem with the FreeBSD implementation of ZFS? I'm not asking this to 
> have someone to point fingers at, but because I want to do some 
> risk-reducing activities. If the problem is in the applications, 
> disabling mmap in those applications will be a workaround. If the 
> problem is with ZFS itself, or with FreeBSD, things start to get 
> interesting (it would need some global switch to turn mmap off, and I'm 
> not sure such a thing is practical/possible).

I think it's a known but outstanding bug in ZFS + mmap.

Kris