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Date: Tue, 10 Apr 2007 14:40:28 -1000
From: Antony Mawer <fbsd-questions@mawer.org>
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Subject: Re: Hardware Raid on Intel DG965OT Motherboard
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On 5/04/2007 1:52 AM, Alexander Anderson wrote:
> Thu, Apr 05, 2007 at 08:52:44 AM, Antony Mawer wrote:
>>> I have Intel D975XBX2 with two on-board SATA RAID controllers: one is Intel
>>> Matrix and the other is Marvell storage. I have FreeBSD 6.2 with RAID-5
>>> using Intel Matrix Storage. It seems to work fine.
>> You may want to re-think that option... according to the ataraid(4) man 
>> page, RAID5 is not functional (ie. you have about as much data safety as 
>> a RAID0 stripe set does):
>>
>>> CAVEATS
>>>     RAID5 is not supported at this time.  Code exists, but it neither uses
>>>     nor maintains parity information.
> 
> The ataraid driver provides *software* RAID. But doesn't Intel Matrix
> Storage gives *hardware* RAID support? How could I tell if software is at
> play?
> 

I'm fairly certain that all ar# devices (ar0, etc) are ataraid-powered, 
and thus are software RAID. If it is a hardware RAID device, typically 
the RAID controller presents a single drive (or one drive for each RAID 
volume) to the OS, and the OS can be ignorant of the number of 
underlying drives.

Also, from man ataraid:

      The ataraid driver can read the following metadata formats:

      ...
      o   Intel MatrixRAID

Which suggests that is is, indeed, just a software RAID setup. That is, 
the BIOS-based bit just writes configuration metadata to the drives, and 
  its up to drivers at the OS level to perform the actual RAID 
operations using that data.

--Antony