[Mailman-Users] MTAs

Brad Knowles brad at stop.mail-abuse.org
Sat Mar 26 03:58:29 CET 2005

At 6:21 PM -0800 2005-03-25, John W. Baxter wrote:

>  Unless softupdates "sees" power outages and hustles the data onto disk
>  (which is probably feasible) it would not be considered MTA-suitable (and
>  Exim does what it can to prevent it, using whatever force to disk calls are
>  available to it).

	The problem is that with modern disks not flushing cache data 
even when they're told to do so, it's virtually impossible to 
guarantee that the data is written before you've lost power.  You're 
completely at the mercy of the hardware, and modern caches these days 
are easily large enough to hold a large number of small files.

	The typical Linux method of using async mounts fairly frequently 
results in filesystem corruption which needs to be corrected with 
fsck, and that can take a long time with a large filesystem.  Yes, 
journaling can ameliorate that problem to a degree, but you still 
need to turn off the async mount if you want as much as they can give 
you in terms of "full protection".

	Softupdates makes sure that the filesystem on disk is always in a 
consistent state, and while a few files/messages may be lost in a 
power outage, the filesystem itself is okay and shouldn't ever need 
to fsck.  Given the modern world we live in and the realities we have 
to deal with, I think that's a pretty good trade-off.

Brad Knowles, <brad at stop.mail-abuse.org>

"Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety."

     -- Benjamin Franklin (1706-1790), reply of the Pennsylvania
     Assembly to the Governor, November 11, 1755

   SAGE member since 1995.  See <http://www.sage.org/> for more info.

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