[linux-lvm] Creating PV over a /dev/mapper device /

Roman Medina-Heigl Hernandez roman at rs-labs.com
Sun Nov 7 14:36:54 UTC 2004

I continued doing some tests upon adding crypt devices to .cache. I
created a PV over /dev/mapper/crypt10, then a VG over the PV. When I
try to create a LV a get an internal error:

jupiter:/etc/lvm# lvcreate -L8G -n home rs-crypt
  Internal error: unknown device-mapper task 16
  Internal error: unknown device-mapper task 16
  Logical volume "home" created

LV seems to be created but I'm scared of using it; not at least
without knowing about the error. What does the former error mean? How
to fix it? Is it reliable to use the LV, despite the internal errors?


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On Sun, 07 Nov 2004 15:01:10 +0100, you wrote:

>I need to create a PV over a /dev/mapper device in order to create a
>crypted LVM system (*) on a Debian Woody with 2.6.9 kernel.
>I encrypted a partition (/dev/hda10) using DM-Crypt, getting
>/dev/mapper/crypt10 device.
>When trying to create PV, I got the following error:
>jupiter:/# pvcreate /dev/mapper/crypt10
>  /dev/mapper/crypt10: Couldn't find device.
>I know how to temporaly fix the problem by adding the device to
>/etc/lvm/.cache. But the problem is that I couldn't get it to be
>permanent. I did several tests modifying /etc/lvm/lvm.conf and
>re-running "vgchange" to re-read changes, but it didn't work.
>I've tried different  lvm.conf configs like:
>filter = [ "a|/dev/mapper/crypt.*|" ]
>(cause I'd like to have crypt10, crypt11 and so on)
>filter = [ "a|/dev/mapper/crypt10|" ]
>filter = [ "a/.*/" ]
>I mixed them with other directives like:
>scan = [ "/dev" ]
>scan = [ "/dev/mapper" ]
>scan = [ "/dev/mapper" "/dev" ]
>Nevertheless, when running vgscan, .cache is re-built without my crypt
>device. What am I doing wrong? Is there any limitation on devices
>scanned by vgscan?
>I'm using this version of LVM:
>jupiter:/# lvm version
>  LVM version:     2.00.21 (2004-08-19)
>  Library version: 1.00.15-ioctl (2004-04-07)
>  Driver version:  4.1.0
>(*) My idea of Crypted LVM system is to have crypted PVs and then
>building LVM over them. This way I got total flexibility provided by
>LVM and the security based on encryption (eg: I can extend/reduce a
>live&mounted crypted fs on-the-fly). Anyone using a similar setup and
>could/want to provide more ideas or feeback about this?
> Saludos,
> --Roman

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