[CentOS] Re: A question about RAID and partitions

[Miguel Medalha]

> Raid devices created on partitions would most likely be software raid as I 
> am
> not sure if you should create partitions on a software raid device, 
> although
> linux would probably let you.. The technology is mature and sound, and the
> processor load is not that great.
> Partitions on top of raid devices would most likely be hardware raid. Some
> devices are better than others, not just the hardware, but the driver 
> support.
>
> You can not answer your question that easily, though. The "type" of raid
> device you create is what will tell you how recoverable it is. A stripe or
> raid 0 is not resilient at all. The loss of one drive will destroy your 
> data.
> How much you can recover would depend on the size of the stripes and the 
> size
> of the data. A mirror or raid 1 is infinitely more recoverable, because a
> complete copy of the data is on each drive.
> Raid 5 or better has a somewhat less chance of survival, but is better 
> than
> raid 0 chance of surviving.
> None of them would be reliable enough to use without some sort of backup.
> Data security shouldn't depend on the type of or lack of raid. Data is 
> secured
> by limiting access.
> The better performing raid types aren't always the best for survivability.
>

Yes, I know all of that...
Either you didn't understand my question or I didn't express myself  well (I 
admit to the latter).
What I meant was: the same type of RAID considered, which situation would 
have been proved better:

- RAID devices created on top of partitions or partitions created on top of 
RAID devices. (I am, of course, talking about Linux software RAID).

And that under the three aspects of performance (CPU utilization, disk 
transfer rate, etc), data security and ability to recover from a disk crash.

The mdadm device, the kernel and the hardware relate to each other in ways 
that *may* make a difference according to the relative order in which the 
partitions and RAID devices are created. (I am assuming EXT3 partitions 
here.) I thought that someone here might have made that experience and would 
be able to tell me, tell us, something about it.

Thank you!