Re: [linux-lvm] Powerfailure and snapshot consistency

[Ron Johnson <ron.l.johnson@cox.net>]

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