On Sat, Oct 29, 2011 at 10:26 AM, NeilBrown <neilb@xxxxxxx> wrote:
> On Sat, 29 Oct 2011 08:49:09 +0400 CoolCold <coolthecold@xxxxxxxxx> wrote:
>
>> Hello!
>>
>> There is holywar once again on nginx maillist about standalone drives
>> vs raid1 arrays for serving static files. By standalone drives it is
>> assumed that file "Filename1" exist on /mnt/disk1, /mnt/disk2,
>> /mnt/diskN where /mnt/diskX is mountpoint for drives /dev/sdY.
>
> If you want fast reads, then use RAID0 if you don't care about losing your
> data, and RAID10 in 'far' mode if you want RAID protection.
>
>>
>> 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.
Neil, thanks for clearing it out!
>
> NeilBrown
>
--
Best regards,
[COOLCOLD-RIPN]
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