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Re: [linux-lvm] Powerfailure and snapshot consistency



On 03/28/2011 12:54 PM, Stuart D. Gathman wrote:
On Mon, 28 Mar 2011, Les Mikesell wrote:

On 3/26/2011 11:07 AM, Stuart D. Gathman wrote:

Is there some non-destructive diagnostic that can tell you if a
running machine can or can't manage write ordering correctly through
all of its software and hardware layers?

http://blog.nirkabel.org/2008/12/07/ext3-write-barriers-and-write-caching/

The above mentions a test program that demonstrates the ext3 weakness.
You should be able to run it in a test VM, and destroy (virtual power off)
the VM. When the barrier=1 mount option is turned on, the mapper is
supposed
to log a warning if this is not supported at some level. There appear to
be disks, however, with hardware write caching that do not correct support
barriers. You must turn off hardware write caching on these models.


"Why did our reports sudden take 85 hours to run?"

--
"Neither the wisest constitution nor the wisest laws will secure
the liberty and happiness of a people whose manners are universally
corrupt."
Samuel Adams, essay in The Public Advertiser, 1749


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