# /dev/mapper empty. udev or mdev fault ?

## Darwish

Hi.

I'm in the installation and configuration of gentoo for several days now. It looks like a clever linux distribution but I dont understand how it's possible to get a LiveCD with plenty of autodection perfectly up and running, but no automated procedure to get the system operationnal on my hard drive without hours of configuration and a few call for help.

The laptop is a Sony VaioZ with 2 SSD drives in raid 0. fakeraid (intel controller)

I compiled a 2.6.38 kernel.

the baselayout 2 has been emerged.

I boot with "dodmraid" as argument to the kernel.

The root partition gets mounted.

mdev starts.

Everything under /dev/mapper disappear, and apparently, udev populate /dev/ with /dev/dm-0 to 10.

openRC mostly fails because the device aren't available. Linux starts in degradated mode.

# I can NOT mount maually any of the /dev/dm-x drive. This throws a /dev/mapper/isw_...VolumeX not found. The root partition is mounted, but the device file is no longer reachable.

dmraid -ay fails stating it's already started

I read tons of documents to understand what I am doing. The single clue I have at this point is that mdev or udev are responsible for this error.

On a first shot to install gentoo on this laptop, I was thrown to the shell during root'partition detection time, still the /dev/mapper/ directory was ok.

any idea or shall I just pick an other distro ?

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## NeddySeagoon

Darwish,

dm-raid is not straight forward to set up and there are lots of reasons for not using it.

The only reason to use dm-raid in Linux is that windows must share the raid set.

For a linux only install, kernel raid is a much better choice.

It sounds like there is a problem with the handover from your initrd root to your real root.

The initrd must load the dm-raid module for your kernel and start dm-raid or your root would not mount.

At the piviot root step, right at the end of the initrd init script, your real root becomes root. At that instant, only root is mounted, /dev is not populated and udev has not even been started.

Its just the kernel and its real_root filesystem.

Look at rc-update show and ensure you have device-mapper in the boot runlevel.  I have a feeling that its been merged with lvm, so if you don't have device-mapper at all, use lvm.

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## Darwish

Thank you very much NeddySeagoon, you saved my day.

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## Hu

 *Darwish wrote:*   

> Thank you very much NeddySeagoon, you saved my day.

 For the benefit of future readers, could you explain what key changes you made after reading Neddy's post?  I suspect it is the remark about installing lvm, but would prefer to get this recorded explicitly.

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## Darwish

I followed Neddy's intuition 

 # rc-update

Showed the device-mapper was missing at the boot run level.

 # rc-update add lvm boot

did the magic

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