Mailinglist Archive: opensuse (1196 mails)

[Greg Freemyer <greg.freemyer@xxxxxxxxx>]

On Thu, Jan 28, 2010 at 4:38 PM, Carlos E. R.
<robin.listas@xxxxxxxxxxxxxx> wrote:
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> On Thursday, 2010-01-28 at 09:12 +0100, Per Jessen wrote:
>
> > FYI, mdraid will do that too, no big deal. Isn't that the whole point? I
> > think the primary difference between the two is that mdraid takes up
> > CPU cycles doing the mirroring, dmraid does not.
>
> Both do, AFAIK. Motherboard, bios raid, is not a real hardware raid, it
> needs a driver that does the real work in the cpu, with some help from the
> chipset. That's why it is called "fake raid".
>
> - -- Cheers,
>       Carlos E. R.

I don't know the specifics, but mdraid for sure and possibly dmraid
have been getting updates in the last year or so to offload the parity
logic.  I assume that some raid cards now expose their xor engine and
thus the data blocks can be sent to them to handle the xor logic.

The patches I noticed were for IBM hardware iirc.

I think the really big difference between dmraid and mdraid is
compatibility.  MS Windows only supports the equivalent of dmraid, so
if you want to create a dual boot raid system, you need to go that
way.

If Windows is not a concern, I think mdraid is the obvious choice but
there may be some subtleties I don't know about.

Greg
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