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

[Ivan Sergio Borgonovo]

On Wed, 1 Mar 2006 09:40:30 -0800
Rick Moen <rick at linuxmafia.com> wrote:

> Quoting Ivan Sergio Borgonovo (mail at webthatworks.it):

> > - While it is clear that fakeraid ctls use the cpu to do raid
> > stuff it is not clear if *all* the job is done by the cpu.
> > http://www.gamepc.com/labs/view_content.asp?id=eoyraid&page=6&cookie%5Ftest=1
> > this table *implicitly suggests* that eg. in sil all raid levels
> > supported excluding raid 5 are hardware and raid 5 is software, in
> > AMCC all the raid levels including raid 5 are hardware.

> AMCC (better known as 3Ware) is not fakeraid, but rather real
> hardware RAID.

OK.... but if nvidia and/or sil don't have hw support for raid the above page would be a bit misleading.

> > - looking at the c code in the sata_sil and sata_nv drivers there
> > is no reference to raid. That means that even if there was a bit
> > of hardware support for raid in those ctls Linux is not able to
> > exploit it at the moment.

> No.  That just means that support for fakeraid is (in the standard
> Linux kernel 2.6.x model) modularised into the dmraid collection of
> subdrivers, rather than being included in block device drivers.
> The two you mention (above) are block device drivers.

Correct. But looking at dmraid docs and source code for at least nvidia and sil seems to confirm my hypothesis that dmraid just deals with metadata, "virtual" device discovery and creation.

> > - once dmraid will be part of debian install my preference may
> > change in favour of the most open driver that at this moment
> > seems to be sil.

> I honestly don't know whether Debian's precompiled 2.6 kernels
> include the dmraid code.  However, it's not very difficult

dm-mod is compiled in the amd64 but dmraid is missing. modprobe dm-mod doesn't help partman to see BIOS raid sets.

> (post-installation) to compile a debianised kernel, FYI:  You'll
> find some guides here: "Information" on
> http://linuxmafia.com/kb/Debian/  Of course, it's probably handy to

Is something I'd prefer not to be obliged to learn. But I bet I'll apreciate your pointer once I'll be obliged.

> have that _during_ OS installation.  ;->   I list a large number of

Exactly.

> See my "Installers" page:  There is a _lot_ more than just one
> Debian installer image -- even for sid AMD64 (though that's
> admittedly stretching the point a little).
> 
> (A throughly determined person would put in a temporary additional
> hard drive without RAID striping, install Debian onto that, fetch
> or build a kernel supporting all desired hardware, and then migrate
> the system onto the striped set.  However, obviously that _would_
> be a pain in the neck.)

Interesting. I gave a look and there were no installers that could let me install sid with dmraid support. Anyway I saw newer amd64 netinstall then the one I burned... but judging from the most recent info I found on Debian Installer:
http://wiki.debian.org/DebianInstaller/FAQ#head-a5623cd5a3ec3d8d6a1eef09e3e4c00f911f8b18
http://lists.debian.org/debian-boot/2005/11/msg00297.html
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=350250
still no support.

After reading more carefully this:
http://xtronics.com/reference/SATA-RAID-debian-for-2.6.html
expecially the "Configure grub to boot from both drives" and "Q & As" sections I understood that actually there is no need for BIOS support for reconstructing a soft RAID set.
I wonder if the "smart" grub configuration is automatically done by the d-i once you put on RAID grub and if it can work for other RAID levels...

Gentoo seems to have precompiled images that support dmraid... but comparatively Debian install without dmraid support is still easier than Gentoo install.

BTW this link on your kb/Installer page seems dead:
http://debian-amd64.alioth.debian.org/install-images/

-- 
Ivan Sergio Borgonovo