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

[Michael Orlitzky <michael@orlitzky.com>]

On 07/18/2011 09:26 PM, Jeff Cranmer wrote:
> Hi all,
> 
> After cleaning off my Opensuse O.S. and installing Gentoo, I'm having
> trouble getting my 3-disk nvidia SATA raid5 array back on line.
> 
> The gentoo OS is on a separate non-raid IDE disk, and I can see the
> three individual disks which make up the raid array (/dev/sda, /dev/sdb
> and /dev/sdc).  Unfortunately, the system does not seem to be able to
> detect the raid array, and dmesg shows no md disks detected or mounted.

Make sure your kernel supports RAID, and RAID5 (they're separate
options). Then emerge mdadm. Once you get it up and running once, you
can dump the current config to /etc/mdadm.conf so you don't have to
assemble it again. Then add mdadm to the boot runlevel.

# mdadm --assemble --help
Usage: mdadm --assemble device options...
       mdadm --assemble --scan options...

This usage assembles one or more raid arrays from pre-existing
components. For each array, mdadm needs to know the md device, the
identity of the array, and a number of sub devices. These can be found
in a number of ways.

The md device is either given on the command line or is found listed
in the config file. The array identity is determined either from the
--uuid or --super-minor commandline arguments, from the config file,
or from the first component device on the command line.

The different combinations of these are as follows:
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.

If an explicit identity is given with --uuid or --super-minor, then
only devices with a superblock which matches that identity is
considered, otherwise every device listed is considered.

If the --scan option is given, and no devices are listed, then
every array listed in the config file is considered for assembly.
The identity of candidate devices are determined from the config file.

If the --scan option is given as well as one or more devices, then
Those devices are md devices that are to be assembled. Their identity
and components are determined from the config file.

If mdadm can not find all of the components for an array, it will
assemble it but not activate it unless --run or --scan is given. To
preserve this behaviour even with --scan, add --no-degraded. Note that
"all of the components" means as many as were present the last time the
array was running as recorded in the superblock. If the array was
already degraded, and the missing device is not a new problem, it will
still be assembled. It is only newly missing devices that cause the
array not to be started.