Re: Problems with Promise PDC 20265 raid on ASUS Motherboard
Roberto Sanchez <rcsanchez97@yahoo.es> wrote:
>> Don't use PDC20265 RAID. Instead, use software RAID1. It is much
>> faster. And safer, probably.
>
> How is that possible? The point of the hardware RAID is to hide the
> implementation from the OS. The OS addresses the logical device and
> the chipset takes care of the mirrorring/striping/whatever.
Your were right if you had hardware RAID. But you haven't got.
This cheap Promise controllers are just plain simple IDE controllers. The
RAID functionality only is implemented by software and nothing else. If you
use e.g. MS-DOS the software in the controller BIOS (read: your computer's
CPU) does the job and if you use any protected mode OS like Linux oder
newer versions of MS-Windows a normal device driver (read: your computer's
CPU again) has to do all the work.
It's really plain simple: You get what you pay for.
> For a software RAID, IIRC, the OS has to legwork, meaning that for a
> mirror array it will send the daya to both disks.
Just the same with your PDC in which case the driver has to take care of
this.
> I don't believe there is a major performance difference for striping,
> especially when you have only diks and they are different controllers,
> but I still think you are wrong for the most part.
Only you were wrong to believe you get hardware RAID for that money.
You basically can now choose to use the software RAID of the PDC driver
or the more general generic linux software RAID. I would recommend the
latter.
Cheers,
Marcus
--
It is easier to fix Unix than to live with NT.
eMail: m@followup-to.de
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