Write cache

Write cache

[mark delfman]

Hi

Is there any way to use an MD RAID in write through mode?  I
appreciate that there is a performance impact but this is important
from a security prospective....

The likelihood is that I would use RAID0 (I know this sounds like a
contradiction to the above, but the ‘drives’ are probably hardware
RAIDs).  But may use standard RAID6.

I cannot see any way to disable write cache in MD, but I am hopefully
I am simply missing something obvious.

I appreciate any feedback....

Thanks, Mark
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Re: Write cache

[Neil Brown]

On Thu, 2 Dec 2010 15:58:51 +0000 mark delfman <markdelfman@googlemail.com>
wrote:

> Hi
> 
> Is there any way to use an MD RAID in write through mode?  I
> appreciate that there is a performance impact but this is important
> from a security prospective....

MD RAID does work in write-through mode.  I have occasionally thought about
adding a write-back mode which would make sense now that we have a sensible
flushing infrastructure in Linux.  But I haven't implemented it.

> 
> The likelihood is that I would use RAID0 (I know this sounds like a
> contradiction to the above, but the ‘drives’ are probably hardware
> RAIDs).  But may use standard RAID6.

RAID0 doesn't do any caching at all.

> 
> I cannot see any way to disable write cache in MD, but I am hopefully
> I am simply missing something obvious.

Why do you think these is a write-behind cache in MD ??

NeilBrown



> 
> I appreciate any feedback....
> 
> Thanks, Mark
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> the body of a message to majordomo@vger.kernel.org
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Re: Write cache

[mark delfman]

Hi Neil,

Actually I made a silly presumption simply because MD is so fast
compared to most of the hardware raids I am testing – so I simple
presumed it was using write cache without really investigating it well
enough

Thank you for the feedback!



On Fri, Dec 3, 2010 at 1:27 AM, Neil Brown <neilb@suse.de> wrote:
> On Thu, 2 Dec 2010 15:58:51 +0000 mark delfman <markdelfman@googlemail.com>
> wrote:
>
>> Hi
>>
>> Is there any way to use an MD RAID in write through mode?  I
>> appreciate that there is a performance impact but this is important
>> from a security prospective....
>
> MD RAID does work in write-through mode.  I have occasionally thought about
> adding a write-back mode which would make sense now that we have a sensible
> flushing infrastructure in Linux.  But I haven't implemented it.
>
>>
>> The likelihood is that I would use RAID0 (I know this sounds like a
>> contradiction to the above, but the ‘drives’ are probably hardware
>> RAIDs).  But may use standard RAID6.
>
> RAID0 doesn't do any caching at all.
>
>>
>> I cannot see any way to disable write cache in MD, but I am hopefully
>> I am simply missing something obvious.
>
> Why do you think these is a write-behind cache in MD ??
>
> NeilBrown
>
>
>
>>
>> I appreciate any feedback....
>>
>> Thanks, Mark
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>
>
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