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Re: LVM in LVM

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On Mon, 16 Sep 2024, Steve Keller wrote:

> In older Debian releases, I think at least until Debian 9, it was
> possible to access PVs and LVs which are stored in a LV.  The PV
> inside the containing LV could be displayed and activated with
> vgdisplay(8) and vgchange(8).
>
> This scenario makes sense if you have a LV for a VM guest, that uses
> LVM inside, and when you need to access file systems in the guest from
> the host (while the guest is shutdown).
>
> I don't see how this can be done in the current Debian 12.
>
> Steve
>
>
Not sure because I've previously battled the opposite problem but I'd
start here in lvm.conf

         # Configuration option devices/sysfs_scan.
         # Restrict device scanning to block devices appearing in sysfs.
         # This is a quick way of filtering out block devices that are
         # not
         # present on the system. sysfs must be part of the kernel and
         # mounted.)
         sysfs_scan = 1

         # Configuration option devices/scan_lvs.
         # Scan LVM LVs for layered PVs, allowing LVs to be used as PVs.
         # When 1, LVM will detect PVs layered on LVs, and caution must
         # be
         # taken to avoid a host accessing a layered VG that may not
         # belong
         # to it, e.g. from a guest image. This generally requires
         # excluding
         # the LVs with device filters. Also, when this setting is
         # enabled,
         # every LVM command will scan every active LV on the system
         # (unless
         # filtered), which can cause performance problems on systems
         # with
         # many active LVs. When this setting is 0, LVM will not detect
         # or
         # use PVs that exist on LVs, and will not allow a PV to be
         # created on
         # an LV. The LVs are ignored using a built in device filter that
         # identifies and excludes LVs.
         scan_lvs = 0

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LVM in LVM Steve Keller <keller.steve@gmx.de> - 2024-09-16 11:40 +0200
  Re: LVM in LVM Tim Woodall <debianuser@woodall.me.uk> - 2024-09-16 12:50 +0200
    Re: LVM in LVM Steve Keller <keller.steve@gmx.de> - 2024-09-20 11:30 +0200
  Re: LVM in LVM Andy Smith <andy@strugglers.net> - 2024-09-16 18:50 +0200

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