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Date: Wed, 18 Jan 2006 15:06:47 +0800
From: Max Waterman <davidmaxwaterman+kernel@fastmail.co.uk>
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To: "Jeff V. Merkey" <jmerkey@wolfmountaingroup.com>
CC: linux-kernel@vger.kernel.org
Subject: Re: io performance...
References: <43CB4CC3.4030904@fastmail.co.uk> <43CDAFE3.8050203@fastmail.co.uk> <43CDC44E.6080808@wolfmountaingroup.com> <43CDCD9F.5050500@fastmail.co.uk> <43CDC607.2040501@wolfmountaingroup.com>
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Jeff V. Merkey wrote:
> Max Waterman wrote:
> 
>> Jeff V. Merkey wrote:
>>
>>> Max Waterman wrote:
>>>
>>>> One further question. I get these messages 'in' dmesg :
>>>>
>>>> sda: asking for cache data failed
>>>> sda: assuming drive cache: write through
>>>>
>>>> How can I force it to be 'write back'?
>>>
>>>
>>>
>>>
>>> Forcing write back is a very bad idea unless you have a battery 
>>> backed up RAID controller.  
>>
>>
>> We do.
>>
>> In any case, I wonder what the consequences of assuming 'write 
>> through' when the array is configured as 'write back'? Is it just 
>> different settings for different caches?
> 
> 
> It is.  This is something that should be configured in a RAID 
> controller.  OS should always be write through.

Ok, thanks for clearing that up, though I now wonder why the message is 
there.

<shrug>

Max.

> 
> Jeff
> 
>>
>> Max.
>>
>>> Jeff
>>>
>>>>
>>>> Max.
>>>> -
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>>
>>
>