[svlug] summary of nvidia/sil soft raid & Linux soft raid

Ivan Sergio Borgonovo mail at webthatworks.it
Mon Mar 13 17:06:15 PST 2006

On Mon, 13 Mar 2006 13:04:07 -0800
Rick Moen <rick at linuxmafia.com> wrote:

> [picking up the earlier but now-again-relevant SATA thread:]
> Quoting Ivan Sergio Borgonovo (mail at webthatworks.it):
> > Rick Moen <rick at linuxmafia.com> wrote:
> > > AMCC (better known as 3Ware) is not fakeraid, but rather real
> > > hardware RAID.
> [Referring to 
> http://www.gamepc.com/labs/view_content.asp?id=eoyraid&page=6&cookie%5Ftest=1:]
> > OK.... but if nvidia and/or sil don't have hw support for raid the
> > above page would be a bit misleading.
> There's still a lot of confusion about what is real hardware RAID and
> what isn't.  The Nvidia and SiI chipsets are part of a growing family of
> hardware capable of BIOS-assisted software RAID.  The BIOS functionality
> typically supports booting from striped sets, and in most cases also the
> creation of such striped sets.  Aside from that, _all_ RAID
> functionality must be furnished (if at all) by driver software.  This
> concept has been dubbed "fakeraid" by the denizens of
> comp.os.linux.hardware, and I've adopted the term for my page because
> it's a useful distinction.

OK... different levels of hardness:

1) really software raid like md
2) software raid with BIOS that take care of reconstructing sets and writing metadata. After POST raid is done by OS/drivers by the CPU 
3) hardware assisted raid. You still need drivers and most of the job is done by the cpu... but there is small bit of work done by the chipset.
4) true hardware raid. All the job is done by the ctl, the OS just see 1 disk.

I was wondering if the 3rd category really exists. Maybe the nvidia or sil provide at least hardware crc or xorring... or maybe they don't and everything is done by the CPU.

I can't understand clearly if sil or nvidia are in category 2 or 3.
Looking at the source of Linux dmraid they should be in category 2, but maybe the drivers are incomplete for lack of documentation. Maybe they are in category 3 as gamepc seems to suggest in the above url.

BTW... I think I already wrote it in previous emails... you were asking about nvidia ctl...
Another point it has over sil... is that the driver support queueing.

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