On Sun, Oct 30, 2011 at 4:36 PM, John Robinson
<john.robinson@xxxxxxxxxxxxxxxx> wrote:
> On 29/10/2011 07:26, NeilBrown wrote:
>>
>> On Sat, 29 Oct 2011 08:49:09 +0400 CoolCold<coolthecold@xxxxxxxxx> wrote:
>
> [...]
>>>
>>> As there are some pros and cons on both sides (at least theoretically)
>>> I have dumb question - let's say our array md1 consists on 3 drives -
>>> /dev/sd{a,b,c} - and when data read from md1 occurs, which block is
>>> cached in VFS (or may be other cache in system, it would be nice to
>>> know which part of system is doing caching) - the block from md1
>>> itself or from certain drive? If it is drive-based block cache, it's
>>> gonna be potentially memory wasting to keep 3 similar data copies, so
>>> I assume md does data reads with something like O_DIRECT flag, but as
>>> I 1) don't know C 2) don't know kernel, I'm asking this on the list to
>>> make this clean for myself.
>>
>> The kernel caches pages of files, not pages of devices.
>> It doesn't matter where the page of data came from - it is the page of a
>> file
>> that is cached.
>
> I suppose if the user was silly enough to mount the same filesystem from
> both md1 and sd{a,b,c} simultaneously then there could be duplication of
> caching, but as I say I think that'd be a silly configuration :-)
Hehe, this is not the situation I'm looking through, there is no
vaccine against shooting in own leg ;)
>
> Cheers,
>
> John.
>
>
--
Best regards,
[COOLCOLD-RIPN]
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