[pve-devel] move disk to LVM

[Wolfgang Bumiller]

On Fri, Feb 17, 2017 at 01:59:47AM +0100, Michael Rasmussen wrote:
> On Thu, 16 Feb 2017 07:50:18 +0100 (CET)
> Dietmar Maurer <dietmar at proxmox.com> wrote:
> 
> > 
> > I am not aware of any decision, and wipe_signatures_when_zeroing_new_lvs
> > is set to 1. Maybe we need to add the -Z flag?
> > 
> It seems this has no effect since the lvcreate command is run without
> terminal in which case lvcreate will skip waiting for input and
> fallback to leave the signature on the disk.

I just tested it and it seems lvcreate's output is actually just wrong:

Run 1: create volume, remember its location, create a partition
  # lvcreate -L 1G -n test pve </dev/null
    Logical volume "test" created.

  # dmsetup table pve-test
  0 2097152 linear 8:35 916662272

  # sgdisk -n0:1M:10M /dev/pve/test
  Creating new GPT entries.
  Warning: The kernel is still using the old partition table.
  The new table will be used at the next reboot.
  The operation has completed successfully.

  # fdisk -l /dev/pve/test
  (...)
  Device         Start   End Sectors Size Type
  /dev/pve/test1  2048 20480   18433   9M Linux filesystem

  # lvremove pve/test
  Do you really want to remove active logical volume test? [y/n]: y
    Logical volume "test" successfully removed

Run 2: recreate the volume without wiping to verify this is working
  # lvcreate -Wn -Zn -L 1G -n test pve </dev/null
    WARNING: Logical volume pve/test not zeroed.
    Logical volume "test" created.

  # dmsetup table pve-test
  0 2097152 linear 8:35 916662272

  # fdisk -l /dev/pve/test
  (...)
  Device         Start   End Sectors Size Type
  /dev/pve/test1  2048 20480   18433   9M Linux filesystem

  # lvremove pve/test
  Do you really want to remove active logical volume test? [y/n]: y
    Logical volume "test" successfully removed

Note that `dmsetup table pve-test` showed the same output and `fdisk -l` 
gave us the partition table.

Run 3: recreate with wiping enabled
  # lvcreate -Wy -Zy -L 1G -n test pve </dev/null
  WARNING: gpt signature detected on /dev/pve/test at offset 512. Wipe it? [y/n]: n
    Aborted wiping of gpt.
    1 existing signature left on the device.
    Logical volume "test" created.

  # fdisk -l /dev/pve/test
  (...) shows that it's empty

  # dmsetup table pve-test
  0 2097152 linear 8:35 916662272

Note that
  1) This is still the same volume according to `dmsetup table pve-test`
  2) The partition table is empty according to `fdisk -l`
  3) `lvcreate` still claimed it "Aborted wiping of gpt"

(PS: The free_image() code could still use some cleanup though as it
activates the volume regardless of whether it's going to write to it
currently (the 'saferemove' flag).)
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