[linux-lvm] Create Snapshot volume, with sized based on size of original lv

["Michael Schmarck" <michael.schmarck@habmalnefrage.de>]

Hi.

I'd like to create a snapshot volume of eg. /dev/sys/Bilder and
call it /dev/sys/Bilder_snap. Bilder_snap should be 25% the size
of Bilder.

How would I do that?

In lvcreate --help, I find:

$ lvm lvcreate --help
[...]
lvcreate -s|--snapshot
[...]
	{-l|--extents LogicalExtentsNumber[%{VG|LV|PVS|FREE}] |
	 -L|--size LogicalVolumeSize[kKmMgGtTpPeE]}
[...]

$ lvm version
  WARNING: Running as a non-root user. Functionality may be unavailable.
  LVM version:     2.02.36 (2008-04-29)
  Library version: 1.02.24 (2007-12-20)
  /dev/mapper/control: open failed: Keine Berechtigung
  Failure to communicate with kernel device-mapper driver.

Based on the --help output, I tried:

$ sudo lvm lvcreate -s -l 25%LV -n Bilder_snap /dev/sys/Bilder
  Please express size as %VG, %PVS, or %FREE.

Did I do something wrong, or is the output "--help"
just wrong?

Thanks a lot,
Michael
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