Regarding Raid1

[Gaurav Mahajan]

Hi Greg...

Thanks for the valuable info...

I tried to understand a few more concepts.....

I believe that md raid is a software raid,which makes it OS dependent
whereas dmraid can be used to create a hardware raid (fakeRAID) which
is OS independent...

Now, what I fail to understand is that whether mdadm, which is a
software tool for creating software RAID uses device mapper
functionality or not. For example, lets say I create a RAID 1 array
using mdadm, will the read and write operations performed on this
array be passed through the device mapper or is the device mapper
bypassed in this case ? The fact that the device mapper is supposed to
be the lowest layer in the storage stack is what brought this question
to my mind....

Basically, I'm wondering whether md and dm are at the same level or is
dm at the lower level and md at a higher level....

It would be really helpful if you could elaborate on the difference
between the working of md and dm....

Regards,
Gaurav

On Sun, Dec 19, 2010 at 10:48 AM, Mulyadi Santosa
<mulyadi.santosa at gmail.com> wrote:
> Hi Greg.......
>
> On Sun, Dec 19, 2010 at 07:28, Greg Freemyer <greg.freemyer at gmail.com> wrote:
>> Both Raid 10 and Raid 1+0 effectively mean the same.
>>
>> The plus is basically implied unless you want Raid 0+1.  I've never
>> seen that call raid 01.
>>
>> I think the use varies on how you build the array.  If you first build
>> a stripeset, then mirror them as 2 separate steps, then use 1+0.
>>
>> If on the otherhand you make a single call to mdadm (as an example)
>> and tell it do do the work in one step, then it is raid 10.  The
>> advantage of raid 10 over 1+0 is mdadm has several ways internally to
>> build a raid 10 whereas there is basically only one way to build a
>> 1+0..
>
> Thanks for your kind explanation....I'll dig further about it when I
> have time. I never knew 'til this you explained it to me that mdadm
> might have its own way to build 1+0...I always think it always be:
> build mirror, then stripe them....
>
> --
> regards,
>
> Mulyadi Santosa
> Freelance Linux trainer and consultant
>
> blog: the-hydra.blogspot.com
> training: mulyaditraining.blogspot.com
>