Re: [gentoo-user] Problems with Nvidia fake raid array

[Jeff Cranmer]

On Tue, 2011-07-19 at 09:06 -0400, Michael Orlitzky wrote:
> On 07/18/2011 11:08 PM, Jeff Cranmer wrote:
> >
> >
> > Pardon my additional questions before taking the plunge here.
> >
> > So, given that I have three devices, /dev/sda, /dev/sdb and /dev/sdc, if
> > I run the command mdadm --assemble --scan, would this find all the
> > components and create a /dev/md0 disk without damaging the contents of
> > the original RAID array?
>
> If you've got the space and time, a backup can't hurt. Using --scan will
> make it check the config file, but right now, there's probably nothing
> useful in it. This looks like what you want to do to me:
>
>   If the --scan option is not given, then only devices and identities
>   listed on the command line are considered.
>
>   The first device will be the array device, and the remainder will be
>   examined when looking for components.
>
> but I'd figure out where that md0 is coming from (below) first.
>
When I tried mdadm --assemble --scan with nothing uncommented in the
configuration file, I got
mdadm: No arrays found in config file or automatically.
Typing dmesg | grep md0 returned no lines.

There are a couple of lines in dmesg when I run dmesg | grep md:, but
they read
md: linear personality registered for level -1
md: raid0 personality registered for level 0
md: raid1 personality registered for level 1
md: raid10 personality registered for level 10
md: raid6 personality registered for level 6
md: raid5 personality registered for level 5
md: raid4 personality registered for level 4
md: Waiting for all devices to be available before autodetect
md: If you don't use raid, use raid=noautodetect
md: Autodetecting RAID arrays
md: Scanned 0 and added 0 devices
md: autorun...
md: ... autorun DONE.

I think this means that raid5 is set up correctly in the kernel, but it
can't find the raid array.

Next I tried adding a line to the config file:

DEVICE /dev/sda /dev/sdb /dev/sdc
mdadm --assemble --scan returned the same results as before

Next, I tried commenting out the previously added DEVICE line, and
adding
ARRAY /dev/md0 devices=/dev/sda,/dev/sdb,/dev/sdc

mdadm --assemble --scan returns something different
mdadm: /dev/sdb has no superblock - assembly aborted.
>
> > The only item in /dev/mapper is th default 'control' entry.  There is
> > a /dev/md0 item already listed, but presently when I try to mount it, it
> > reports that it is unable to read the superblock.  Would the command
> > above fix this?
>
> Depends. Where'd the md0 come from? You probably have something in your
> logs or dmesg, unless that device was created manually on your old system.
>
>
> > Where is the config file mentioned in your e-mail, and do I need to edit
> > it first to add the three raid disks?
>
> It's /etc/mdadm.conf. You don't need it to create or use the array, but
> you'll want to run mdadm when the machine boots and the config file
> tells it what to do. Once the array is working, you can just do,
>
>   mdadm --detail --scan >> /etc/mdadm.conf
>
mdadm --detail --scan returns no output.

Also, I just checked /dev and md0 is now gone from the list.

Since there are also /dev/sg0, /dev/sg1 and /dev/sg1, I also tried those
instead of /dev/sda, /dev/sdb and /dev/sdc in the ARRAY line, but mdadm
--assemble --scan returned no output

I tried re-booting, but /dev/md0 is now permanently gone.

Does this give you any ideas what I can try next??

Thanks

Jeff