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Andrew Bolster
Asked: 2010-03-25 13:02:43 +0800 CST

Ubuntu Device-mapper seems to be invincible!

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I'm working on a hopefully unrelated question question and I've got to a strange situation.

First: I know very little about the very low level hardware kernel storage driver magix, so I'm hoping a) someone can help and b) someone can explain it to me better.

I've been trying a dozen different configurations of my 2x500GB SATA drives over the past few hours involving switching between ACHI/IDE/RAID in my bios; After each attempt I've reset the bios option, booted into a live CD, deleting partitions and rewriting partition tables left on the drives.

Now, however, I've been sitting with a /dev/mapper/nvidia_XXXXXXX1 that seems to be impossible to kill!

It's the only 'partition' that I see in the Ubuntu install (but I can see the others in parted) but it is only the size of one of the drives, and I know I did not set any RAID levels other than RAID0.

Anyone have any ideas how I can kill this and get back to just two independent IDE drives? Or can anyone convince me of a reason to go the AHCI route?

Many thanks in advance.

Update Thanks to you guys this was sorted, and I've updated my blog with a summary walkthrough

hardware hard-drive linux ubuntu device

3 Answers

  1. Best Answer

    Thanks to wazoox for eliminating a possibility, but I found what works for me.

    After a bit of experimenting, I tried

    $dmraid -r

    so see what raid sets were set up, then did

    $dmraid -x

    but was presented with

    ERROR: Raid set deletion is not supported in "nvidia" format

    Googled this and found this forum post that told me to do this;

    $dmraid -rE

    And that went through, rebooted, hoped, waited (well, while i was waiting, set the bios back to AHCI), and repartitioned, and all of (this particular issue) was well again. Hope this helps someone else down the line!

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  2. You definitely must use AHCI. This is the native SATA controller mode, it provides enormous performance gains compared to the funky IDE emulation. "RAID" on motherboards is basically a sham, hiding a software RAID through a windows driver, and has absolutely zero effect under Linux. If you want RAID, use software RAID, it works great.

    The "/dev/mapper/xxx" stuff probably is an LVM logical volume created by some partial installation. Open a console and see what "lvdisplay" shows. If there's some LVs, delete them with 

    lvremove /dev/whatever

    Then check for volumes groups and remove them : get the list with

    vgdisplay

    then kill with

    vgremove /dev/whatever

    Finally clean up LVM physical volumes :

    lvdisplay

    then 

    lvremove /dev/whatever

    For reference, LVM manages disks partitions as "physical volumes", aggregates them in "volume groups", then allows you to make "logical volumes" on them. See LVM on wikipedia for more gory details.

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  3. Device mapper creates references to partitions or devices, and associates a UUID that is different to the one seen in partition managers. Its not a new or separate device, its just a new reference. You can just get rid of the reference, there is no need to clean up your partitions or devices.

    I wanted to remove a device that appeared in my file browser, because it is from another OS that i dont want to access from Ubuntu. (Im using a triple boot UEFI laptop.) I wanted to remove the device mapper device reference in my file browser.

    The file browser showed me the UUID of the device

    $ sudo blkid

    --> lists all the devices and showed me the UUID came from device mapper

    Hiding the partitions using /etc/udev/rules.d/ didnt work.

    The answer by wazoox worked for me, to remove the device mapper reference.

    $ sudo lvdisplay

    --> showed the persistently displayed device, and another of same OS

    $ sudo vgscan

    --> showed me that i had one group, corresponding to the OS of the device

    $ sudo vgremove groupname

    --> deleted the group (change groupname to yours, no quotes)

    When i reopened the file browser, that persistent device was gone. When i rebooted, the device didnt reappear in my browser.

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