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From: Bob Friesenhahn <bfriesen@simple.dallas.tx.us>
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Cc: freebsd-fs@freebsd.org
Subject: Re: ZFS RaidZ2 with 24 drives?
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On Fri, 1 Jan 2010, Danny Carroll wrote:
>
> You do not have this protection when ZFS has access to the raw devices.
> Even worse if the devices write cache is turned on.

This statement does not appear to be true.  ZFS will always request 
that devices flush their cache.  The only time there is no 
"protection" is if the device ignores that flush request and the cache 
is volatile.  Controller battery-backed RAM is useful since the 
controller can respond to the cache flush request once the data is in 
battery-backed RAM, thereby dramatically improving write latencies for 
small writes

Bob
--
Bob Friesenhahn
bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/