Converting to EXT4 on encrypted lvm

[Bruno Wolff III]

On Wed, Jul 01, 2009 at 13:05:09 -0600,
  "Andrig T. Miller" <andrig.t.miller at gmail.com> wrote:
> After upgrading to Fedora 11 x86_64, I started to look into converting
> to EXT4 from EXT3.
> 
> My / partition is an lvm that is encrypted (I do have a separate /boot).
> 
> I tried following the instructions using tune2fs -O
> extents,uninit_bg,dir_index /dev/sda2 (my / device and /boot is
> /dev/sda1).
> 
> Finally, I just booted by changing /etc/fstab to specify ext4, which
> works fine, but from reading the various instructions, I won't have
> the new features turned on unless I am able to use tune2fs
> successfully.

You have to point to the block device your file system is on, not the disk
partition. I have used tune2fs on encrypted partitions and the device
is /dev/mapper/luks-someluksuuid . In your case you need to find the lvm
device name used for the file system. I don't know how those look, but
I would expect a device mapper entry for it, so /dev/mapper would be a
good place to look. You'll have a luks entry there as well, but you will
not want to use it as that is the device that lvm is on, not a device
provided by lvm.